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Groups > linux.kernel > #1705149 > unrolled thread
| Started by | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| First post | 2017-08-07 09:20 +0200 |
| Last post | 2017-08-10 13:50 +0200 |
| Articles | 20 on this page of 32 — 4 participants |
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[PATCH v8 00/14] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-08-07 09:20 +0200
[PATCH v8 08/14] lockdep: Make print_circular_bug() aware of crossrelease Byungchul Park <byungchul.park@lge.com> - 2017-08-07 09:20 +0200
[tip:locking/core] locking/lockdep: Make print_circular_bug() aware of crossrelease tip-bot for Byungchul Park <tipbot@zytor.com> - 2017-08-10 14:30 +0200
[PATCH v8 05/14] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-08-07 09:20 +0200
Re: [PATCH v8 05/14] lockdep: Implement crossrelease feature Peter Zijlstra <peterz@infradead.org> - 2017-08-09 16:10 +0200
Re: [PATCH v8 05/14] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-08-10 03:40 +0200
Re: [PATCH v8 05/14] lockdep: Implement crossrelease feature Peter Zijlstra <peterz@infradead.org> - 2017-08-10 11:30 +0200
[tip:locking/core] locking/lockdep: Implement the 'crossrelease' feature tip-bot for Byungchul Park <tipbot@zytor.com> - 2017-08-10 14:30 +0200
[PATCH v8 11/14] lockdep: Apply crossrelease to PG_locked locks Byungchul Park <byungchul.park@lge.com> - 2017-08-07 09:20 +0200
Re: [PATCH v8 11/14] lockdep: Apply crossrelease to PG_locked locks Byungchul Park <byungchul.park@lge.com> - 2017-08-10 03:40 +0200
Re: [PATCH v8 11/14] lockdep: Apply crossrelease to PG_locked locks Peter Zijlstra <peterz@infradead.org> - 2017-08-10 11:30 +0200
[PATCH v8 10/14] pagemap.h: Remove trailing white space Byungchul Park <byungchul.park@lge.com> - 2017-08-07 09:20 +0200
[PATCH v8 07/14] lockdep: Handle non(or multi)-acquisition of a crosslock Byungchul Park <byungchul.park@lge.com> - 2017-08-07 09:20 +0200
[tip:locking/core] locking/lockdep: Handle non(or multi)-acquisition of a crosslock tip-bot for Byungchul Park <tipbot@zytor.com> - 2017-08-10 14:30 +0200
[PATCH v8 12/14] lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked Byungchul Park <byungchul.park@lge.com> - 2017-08-07 09:20 +0200
[PATCH v8 14/14] lockdep: Crossrelease feature documentation Byungchul Park <byungchul.park@lge.com> - 2017-08-07 09:20 +0200
[tip:locking/core] locking/lockdep: Add 'crossrelease' feature documentation tip-bot for Byungchul Park <tipbot@zytor.com> - 2017-08-10 14:30 +0200
[PATCH v8 09/14] lockdep: Apply crossrelease to completions Byungchul Park <byungchul.park@lge.com> - 2017-08-07 09:20 +0200
Re: [PATCH v8 09/14] lockdep: Apply crossrelease to completions Peter Zijlstra <peterz@infradead.org> - 2017-08-09 12:00 +0200
Re: [PATCH v8 09/14] lockdep: Apply crossrelease to completions Peter Zijlstra <peterz@infradead.org> - 2017-08-09 12:30 +0200
Re: [PATCH v8 09/14] lockdep: Apply crossrelease to completions Byungchul Park <byungchul.park@lge.com> - 2017-08-10 03:30 +0200
[tip:locking/core] locking/lockdep: Apply crossrelease to completions tip-bot for Byungchul Park <tipbot@zytor.com> - 2017-08-10 14:30 +0200
[PATCH v8 04/14] lockdep: Make check_prev_add() able to handle external stack_trace Byungchul Park <byungchul.park@lge.com> - 2017-08-07 09:20 +0200
[tip:locking/core] locking/lockdep: Make check_prev_add() able to handle external stack_trace tip-bot for Byungchul Park <tipbot@zytor.com> - 2017-08-10 14:30 +0200
Re: [PATCH v8 00/14] lockdep: Implement crossrelease feature Peter Zijlstra <peterz@infradead.org> - 2017-08-09 18:00 +0200
Re: [PATCH v8 00/14] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-08-10 03:00 +0200
Re: [PATCH v8 00/14] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-08-10 05:50 +0200
Re: [PATCH v8 00/14] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-08-10 13:00 +0200
Re: [PATCH v8 00/14] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-08-10 11:40 +0200
Re: [PATCH v8 00/14] lockdep: Implement crossrelease feature Peter Zijlstra <peterz@infradead.org> - 2017-08-10 13:00 +0200
Re: [PATCH v8 00/14] lockdep: Implement crossrelease feature Ingo Molnar <mingo@kernel.org> - 2017-08-10 13:20 +0200
Re: [PATCH v8 00/14] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-08-10 13:50 +0200
Page 1 of 2 [1] 2 Next page →
| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-07 09:20 +0200 |
| Subject | [PATCH v8 00/14] lockdep: Implement crossrelease feature |
| Message-ID | <ubKut-59V-3@gated-at.bofh.it> |
Change from v7
- rebase on latest tip/sched/core (Jul 26 2017)
- apply peterz's suggestions
- simplify code of crossrelease_{hist/soft/hard}_{start/end}
- exclude a patch avoiding redundant links
- exclude a patch already applied onto the base
Change from v6
- unwind the ring buffer instead tagging for 'work' context
- introduce hist_id to distinguish every entry of ring buffer
- change the point calling crossrelease_work_start()
- handle cases the ring buffer was overwritten
- change LOCKDEP_CROSSRELEASE config in Kconfig
(select PROVE_LOCKING -> depends on PROVE_LOCKING)
- rename xhlock_used() -> xhlock_valid()
- simplify serveral code (e.g. traversal the ring buffer)
- add/enhance several comments and changelogs
Change from v5
- force XHLOCKS_SIZE to be power of 2 and simplify code
- remove nmi check
- separate an optimization using prev_gen_id with a full changelog
- separate non(multi)-acquisition handling with a full changelog
- replace vmalloc with kmallock(GFP_KERNEL) for xhlocks
- select PROVE_LOCKING when choosing CROSSRELEASE
- clean serveral code (e.g. loose some ifdefferies)
- enhance several comments and changelogs
Change from v4
- rebase on vanilla v4.9 tag
- re-name pend_lock(plock) to hist_lock(xhlock)
- allow overwriting ring buffer for hist_lock
- unwind ring buffer instead of tagging id for each irq
- introduce lockdep_map_cross embedding cross_lock
- make each work of workqueue distinguishable
- enhance comments
(I will update the document at the next spin.)
Change from v3
- reviced document
Change from v2
- rebase on vanilla v4.7 tag
- move lockdep data for page lock from struct page to page_ext
- allocate plocks buffer via vmalloc instead of in struct task
- enhanced comments and document
- optimize performance
- make reporting function crossrelease-aware
Change from v1
- enhanced the document
- removed save_stack_trace() optimizing patch
- made this based on the seperated save_stack_trace patchset
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1182242.html
Can we detect deadlocks below with original lockdep?
Example 1)
PROCESS X PROCESS Y
-------------- --------------
mutext_lock A
lock_page B
lock_page B
mutext_lock A // DEADLOCK
unlock_page B
mutext_unlock A
mutex_unlock A
unlock_page B
where A and B are different lock classes.
No, we cannot.
Example 2)
PROCESS X PROCESS Y PROCESS Z
-------------- -------------- --------------
mutex_lock A
lock_page B
lock_page B
mutext_lock A // DEADLOCK
mutext_unlock A
unlock_page B
(B was held by PROCESS X)
unlock_page B
mutex_unlock A
where A and B are different lock classes.
No, we cannot.
Example 3)
PROCESS X PROCESS Y
-------------- --------------
mutex_lock A
mutex_lock A
wait_for_complete B // DEADLOCK
mutex_unlock A
complete B
mutex_unlock A
where A is a lock class and B is a completion variable.
No, we cannot.
Not only lock operations, but also any operations causing to wait or
spin for something can cause deadlock unless it's eventually *released*
by someone. The important point here is that the waiting or spinning
must be *released* by someone.
Using crossrelease feature, we can check dependency and detect deadlock
possibility not only for typical lock, but also for lock_page(),
wait_for_xxx() and so on, which might be released in any context.
See the last patch including the document for more information.
Byungchul Park (14):
lockdep: Refactor lookup_chain_cache()
lockdep: Add a function building a chain between two classes
lockdep: Change the meaning of check_prev_add()'s return value
lockdep: Make check_prev_add() able to handle external stack_trace
lockdep: Implement crossrelease feature
lockdep: Detect and handle hist_lock ring buffer overwrite
lockdep: Handle non(or multi)-acquisition of a crosslock
lockdep: Make print_circular_bug() aware of crossrelease
lockdep: Apply crossrelease to completions
pagemap.h: Remove trailing white space
lockdep: Apply crossrelease to PG_locked locks
lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked
lockdep: Move data of CONFIG_LOCKDEP_PAGELOCK from page to page_ext
lockdep: Crossrelease feature documentation
Documentation/locking/crossrelease.txt | 874 +++++++++++++++++++++++++++++++++
include/linux/completion.h | 118 ++++-
include/linux/irqflags.h | 24 +-
include/linux/lockdep.h | 150 +++++-
include/linux/mm_types.h | 4 +
include/linux/page-flags.h | 43 +-
include/linux/page_ext.h | 4 +
include/linux/pagemap.h | 125 ++++-
include/linux/sched.h | 11 +
kernel/exit.c | 1 +
kernel/fork.c | 4 +
kernel/locking/lockdep.c | 862 ++++++++++++++++++++++++++++----
kernel/sched/completion.c | 56 ++-
kernel/workqueue.c | 2 +
lib/Kconfig.debug | 29 ++
mm/filemap.c | 73 ++-
mm/page_ext.c | 4 +
17 files changed, 2233 insertions(+), 151 deletions(-)
create mode 100644 Documentation/locking/crossrelease.txt
--
1.9.1
[toc] | [next] | [standalone]
| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-07 09:20 +0200 |
| Subject | [PATCH v8 08/14] lockdep: Make print_circular_bug() aware of crossrelease |
| Message-ID | <ubKuu-59V-23@gated-at.bofh.it> |
| In reply to | #1705149 |
print_circular_bug() reporting circular bug assumes that target hlock is
owned by the current. However, in crossrelease, target hlock can be
owned by other than the current. So the report format needs to be
changed to reflect the change.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
kernel/locking/lockdep.c | 67 +++++++++++++++++++++++++++++++++---------------
1 file changed, 47 insertions(+), 20 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 4eae7dc..a2b6aaa 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1141,22 +1141,41 @@ static inline int __bfs_backwards(struct lock_list *src_entry,
printk(KERN_CONT "\n\n");
}
- printk(" Possible unsafe locking scenario:\n\n");
- printk(" CPU0 CPU1\n");
- printk(" ---- ----\n");
- printk(" lock(");
- __print_lock_name(target);
- printk(KERN_CONT ");\n");
- printk(" lock(");
- __print_lock_name(parent);
- printk(KERN_CONT ");\n");
- printk(" lock(");
- __print_lock_name(target);
- printk(KERN_CONT ");\n");
- printk(" lock(");
- __print_lock_name(source);
- printk(KERN_CONT ");\n");
- printk("\n *** DEADLOCK ***\n\n");
+ if (cross_lock(tgt->instance)) {
+ printk(" Possible unsafe locking scenario by crosslock:\n\n");
+ printk(" CPU0 CPU1\n");
+ printk(" ---- ----\n");
+ printk(" lock(");
+ __print_lock_name(parent);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(target);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(source);
+ printk(KERN_CONT ");\n");
+ printk(" unlock(");
+ __print_lock_name(target);
+ printk(KERN_CONT ");\n");
+ printk("\n *** DEADLOCK ***\n\n");
+ } else {
+ printk(" Possible unsafe locking scenario:\n\n");
+ printk(" CPU0 CPU1\n");
+ printk(" ---- ----\n");
+ printk(" lock(");
+ __print_lock_name(target);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(parent);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(target);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(source);
+ printk(KERN_CONT ");\n");
+ printk("\n *** DEADLOCK ***\n\n");
+ }
}
/*
@@ -1181,7 +1200,12 @@ static inline int __bfs_backwards(struct lock_list *src_entry,
pr_warn("%s/%d is trying to acquire lock:\n",
curr->comm, task_pid_nr(curr));
print_lock(check_src);
- pr_warn("\nbut task is already holding lock:\n");
+
+ if (cross_lock(check_tgt->instance))
+ pr_warn("\nbut now in release context of a crosslock acquired at the following:\n");
+ else
+ pr_warn("\nbut task is already holding lock:\n");
+
print_lock(check_tgt);
pr_warn("\nwhich lock already depends on the new lock.\n\n");
pr_warn("\nthe existing dependency chain (in reverse order) is:\n");
@@ -1199,7 +1223,8 @@ static inline int class_equal(struct lock_list *entry, void *data)
static noinline int print_circular_bug(struct lock_list *this,
struct lock_list *target,
struct held_lock *check_src,
- struct held_lock *check_tgt)
+ struct held_lock *check_tgt,
+ struct stack_trace *trace)
{
struct task_struct *curr = current;
struct lock_list *parent;
@@ -1209,7 +1234,9 @@ static noinline int print_circular_bug(struct lock_list *this,
if (!debug_locks_off_graph_unlock() || debug_locks_silent)
return 0;
- if (!save_trace(&this->trace))
+ if (cross_lock(check_tgt->instance))
+ this->trace = *trace;
+ else if (!save_trace(&this->trace))
return 0;
depth = get_lock_depth(target);
@@ -1853,7 +1880,7 @@ static inline void inc_chains(void)
this.parent = NULL;
ret = check_noncircular(&this, hlock_class(prev), &target_entry);
if (unlikely(!ret))
- return print_circular_bug(&this, target_entry, next, prev);
+ return print_circular_bug(&this, target_entry, next, prev, trace);
else if (unlikely(ret < 0))
return print_bfs_bug(ret);
--
1.9.1
[toc] | [prev] | [next] | [standalone]
| From | tip-bot for Byungchul Park <tipbot@zytor.com> |
|---|---|
| Date | 2017-08-10 14:30 +0200 |
| Subject | [tip:locking/core] locking/lockdep: Make print_circular_bug() aware of crossrelease |
| Message-ID | <ucUL9-5wC-49@gated-at.bofh.it> |
| In reply to | #1705151 |
Commit-ID: 383a4bc88849b804385162e81bf704f8f9690a87
Gitweb: http://git.kernel.org/tip/383a4bc88849b804385162e81bf704f8f9690a87
Author: Byungchul Park <byungchul.park@lge.com>
AuthorDate: Mon, 7 Aug 2017 16:12:55 +0900
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 10 Aug 2017 12:29:09 +0200
locking/lockdep: Make print_circular_bug() aware of crossrelease
print_circular_bug() reporting circular bug assumes that target hlock is
owned by the current. However, in crossrelease, target hlock can be
owned by other than the current. So the report format needs to be
changed to reflect the change.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akpm@linux-foundation.org
Cc: boqun.feng@gmail.com
Cc: kernel-team@lge.com
Cc: kirill@shutemov.name
Cc: npiggin@gmail.com
Cc: walken@google.com
Cc: willy@infradead.org
Link: http://lkml.kernel.org/r/1502089981-21272-9-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/locking/lockdep.c | 67 +++++++++++++++++++++++++++++++++---------------
1 file changed, 47 insertions(+), 20 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 7f97871..1114dc4 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1139,22 +1139,41 @@ print_circular_lock_scenario(struct held_lock *src,
printk(KERN_CONT "\n\n");
}
- printk(" Possible unsafe locking scenario:\n\n");
- printk(" CPU0 CPU1\n");
- printk(" ---- ----\n");
- printk(" lock(");
- __print_lock_name(target);
- printk(KERN_CONT ");\n");
- printk(" lock(");
- __print_lock_name(parent);
- printk(KERN_CONT ");\n");
- printk(" lock(");
- __print_lock_name(target);
- printk(KERN_CONT ");\n");
- printk(" lock(");
- __print_lock_name(source);
- printk(KERN_CONT ");\n");
- printk("\n *** DEADLOCK ***\n\n");
+ if (cross_lock(tgt->instance)) {
+ printk(" Possible unsafe locking scenario by crosslock:\n\n");
+ printk(" CPU0 CPU1\n");
+ printk(" ---- ----\n");
+ printk(" lock(");
+ __print_lock_name(parent);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(target);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(source);
+ printk(KERN_CONT ");\n");
+ printk(" unlock(");
+ __print_lock_name(target);
+ printk(KERN_CONT ");\n");
+ printk("\n *** DEADLOCK ***\n\n");
+ } else {
+ printk(" Possible unsafe locking scenario:\n\n");
+ printk(" CPU0 CPU1\n");
+ printk(" ---- ----\n");
+ printk(" lock(");
+ __print_lock_name(target);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(parent);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(target);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(source);
+ printk(KERN_CONT ");\n");
+ printk("\n *** DEADLOCK ***\n\n");
+ }
}
/*
@@ -1179,7 +1198,12 @@ print_circular_bug_header(struct lock_list *entry, unsigned int depth,
pr_warn("%s/%d is trying to acquire lock:\n",
curr->comm, task_pid_nr(curr));
print_lock(check_src);
- pr_warn("\nbut task is already holding lock:\n");
+
+ if (cross_lock(check_tgt->instance))
+ pr_warn("\nbut now in release context of a crosslock acquired at the following:\n");
+ else
+ pr_warn("\nbut task is already holding lock:\n");
+
print_lock(check_tgt);
pr_warn("\nwhich lock already depends on the new lock.\n\n");
pr_warn("\nthe existing dependency chain (in reverse order) is:\n");
@@ -1197,7 +1221,8 @@ static inline int class_equal(struct lock_list *entry, void *data)
static noinline int print_circular_bug(struct lock_list *this,
struct lock_list *target,
struct held_lock *check_src,
- struct held_lock *check_tgt)
+ struct held_lock *check_tgt,
+ struct stack_trace *trace)
{
struct task_struct *curr = current;
struct lock_list *parent;
@@ -1207,7 +1232,9 @@ static noinline int print_circular_bug(struct lock_list *this,
if (!debug_locks_off_graph_unlock() || debug_locks_silent)
return 0;
- if (!save_trace(&this->trace))
+ if (cross_lock(check_tgt->instance))
+ this->trace = *trace;
+ else if (!save_trace(&this->trace))
return 0;
depth = get_lock_depth(target);
@@ -1864,7 +1891,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
this.parent = NULL;
ret = check_noncircular(&this, hlock_class(prev), &target_entry);
if (unlikely(!ret))
- return print_circular_bug(&this, target_entry, next, prev);
+ return print_circular_bug(&this, target_entry, next, prev, trace);
else if (unlikely(ret < 0))
return print_bfs_bug(ret);
[toc] | [prev] | [next] | [standalone]
| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-07 09:20 +0200 |
| Subject | [PATCH v8 05/14] lockdep: Implement crossrelease feature |
| Message-ID | <ubKuu-59V-17@gated-at.bofh.it> |
| In reply to | #1705149 |
Lockdep is a runtime locking correctness validator that detects and
reports a deadlock or its possibility by checking dependencies between
locks. It's useful since it does not report just an actual deadlock but
also the possibility of a deadlock that has not actually happened yet.
That enables problems to be fixed before they affect real systems.
However, this facility is only applicable to typical locks, such as
spinlocks and mutexes, which are normally released within the context in
which they were acquired. However, synchronization primitives like page
locks or completions, which are allowed to be released in any context,
also create dependencies and can cause a deadlock. So lockdep should
track these locks to do a better job. The 'crossrelease' implementation
makes these primitives also be tracked.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
include/linux/irqflags.h | 24 ++-
include/linux/lockdep.h | 110 +++++++++-
include/linux/sched.h | 8 +
kernel/exit.c | 1 +
kernel/fork.c | 4 +
kernel/locking/lockdep.c | 508 ++++++++++++++++++++++++++++++++++++++++++++---
kernel/workqueue.c | 2 +
lib/Kconfig.debug | 12 ++
8 files changed, 635 insertions(+), 34 deletions(-)
diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 5dd1272..e9ed580 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -23,10 +23,26 @@
# define trace_softirq_context(p) ((p)->softirq_context)
# define trace_hardirqs_enabled(p) ((p)->hardirqs_enabled)
# define trace_softirqs_enabled(p) ((p)->softirqs_enabled)
-# define trace_hardirq_enter() do { current->hardirq_context++; } while (0)
-# define trace_hardirq_exit() do { current->hardirq_context--; } while (0)
-# define lockdep_softirq_enter() do { current->softirq_context++; } while (0)
-# define lockdep_softirq_exit() do { current->softirq_context--; } while (0)
+# define trace_hardirq_enter() \
+do { \
+ current->hardirq_context++; \
+ crossrelease_hist_start(HARD); \
+} while (0)
+# define trace_hardirq_exit() \
+do { \
+ current->hardirq_context--; \
+ crossrelease_hist_end(HARD); \
+} while (0)
+# define lockdep_softirq_enter() \
+do { \
+ current->softirq_context++; \
+ crossrelease_hist_start(SOFT); \
+} while (0)
+# define lockdep_softirq_exit() \
+do { \
+ current->softirq_context--; \
+ crossrelease_hist_end(SOFT); \
+} while (0)
# define INIT_TRACE_IRQFLAGS .softirqs_enabled = 1,
#else
# define trace_hardirqs_on() do { } while (0)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index fffe49f..0c8a1b8 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -155,6 +155,12 @@ struct lockdep_map {
int cpu;
unsigned long ip;
#endif
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+ /*
+ * Whether it's a crosslock.
+ */
+ int cross;
+#endif
};
static inline void lockdep_copy_map(struct lockdep_map *to,
@@ -258,8 +264,62 @@ struct held_lock {
unsigned int hardirqs_off:1;
unsigned int references:12; /* 32 bits */
unsigned int pin_count;
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+ /*
+ * Generation id.
+ *
+ * A value of cross_gen_id will be stored when holding this,
+ * which is globally increased whenever each crosslock is held.
+ */
+ unsigned int gen_id;
+#endif
+};
+
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+#define MAX_XHLOCK_TRACE_ENTRIES 5
+
+/*
+ * This is for keeping locks waiting for commit so that true dependencies
+ * can be added at commit step.
+ */
+struct hist_lock {
+ /*
+ * Seperate stack_trace data. This will be used at commit step.
+ */
+ struct stack_trace trace;
+ unsigned long trace_entries[MAX_XHLOCK_TRACE_ENTRIES];
+
+ /*
+ * Seperate hlock instance. This will be used at commit step.
+ *
+ * TODO: Use a smaller data structure containing only necessary
+ * data. However, we should make lockdep code able to handle the
+ * smaller one first.
+ */
+ struct held_lock hlock;
+};
+
+/*
+ * To initialize a lock as crosslock, lockdep_init_map_crosslock() should
+ * be called instead of lockdep_init_map().
+ */
+struct cross_lock {
+ /*
+ * Seperate hlock instance. This will be used at commit step.
+ *
+ * TODO: Use a smaller data structure containing only necessary
+ * data. However, we should make lockdep code able to handle the
+ * smaller one first.
+ */
+ struct held_lock hlock;
};
+struct lockdep_map_cross {
+ struct lockdep_map map;
+ struct cross_lock xlock;
+};
+#endif
+
/*
* Initialization, self-test and debugging-output methods:
*/
@@ -282,13 +342,6 @@ extern void lockdep_init_map(struct lockdep_map *lock, const char *name,
struct lock_class_key *key, int subclass);
/*
- * To initialize a lockdep_map statically use this macro.
- * Note that _name must not be NULL.
- */
-#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
- { .name = (_name), .key = (void *)(_key), }
-
-/*
* Reinitialize a lock key - for cases where there is special locking or
* special initialization of locks so that the validator gets the scope
* of dependencies wrong: they are either too broad (they need a class-split)
@@ -467,6 +520,49 @@ static inline void lockdep_on(void)
#endif /* !LOCKDEP */
+enum context_t {
+ HARD,
+ SOFT,
+ PROC,
+ CONTEXT_NR,
+};
+
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+extern void lockdep_init_map_crosslock(struct lockdep_map *lock,
+ const char *name,
+ struct lock_class_key *key,
+ int subclass);
+extern void lock_commit_crosslock(struct lockdep_map *lock);
+
+#define STATIC_CROSS_LOCKDEP_MAP_INIT(_name, _key) \
+ { .map.name = (_name), .map.key = (void *)(_key), \
+ .map.cross = 1, }
+
+/*
+ * To initialize a lockdep_map statically use this macro.
+ * Note that _name must not be NULL.
+ */
+#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
+ { .name = (_name), .key = (void *)(_key), .cross = 0, }
+
+extern void crossrelease_hist_start(enum context_t c);
+extern void crossrelease_hist_end(enum context_t c);
+extern void lockdep_init_task(struct task_struct *task);
+extern void lockdep_free_task(struct task_struct *task);
+#else
+/*
+ * To initialize a lockdep_map statically use this macro.
+ * Note that _name must not be NULL.
+ */
+#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
+ { .name = (_name), .key = (void *)(_key), }
+
+static inline void crossrelease_hist_start(enum context_t c) {}
+static inline void crossrelease_hist_end(enum context_t c) {}
+static inline void lockdep_init_task(struct task_struct *task) {}
+static inline void lockdep_free_task(struct task_struct *task) {}
+#endif
+
#ifdef CONFIG_LOCK_STAT
extern void lock_contended(struct lockdep_map *lock, unsigned long ip);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8337e2d..5becef5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -849,6 +849,14 @@ struct task_struct {
gfp_t lockdep_reclaim_gfp;
#endif
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+#define MAX_XHLOCKS_NR 64UL
+ struct hist_lock *xhlocks; /* Crossrelease history locks */
+ unsigned int xhlock_idx;
+ /* For restoring at history boundaries */
+ unsigned int xhlock_idx_hist[CONTEXT_NR];
+#endif
+
#ifdef CONFIG_UBSAN
unsigned int in_ubsan;
#endif
diff --git a/kernel/exit.c b/kernel/exit.c
index c5548fa..fa72d57 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -920,6 +920,7 @@ void __noreturn do_exit(long code)
exit_rcu();
TASKS_RCU(__srcu_read_unlock(&tasks_rcu_exit_srcu, tasks_rcu_i));
+ lockdep_free_task(tsk);
do_task_dead();
}
EXPORT_SYMBOL_GPL(do_exit);
diff --git a/kernel/fork.c b/kernel/fork.c
index 17921b0..cbf2221 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -484,6 +484,8 @@ void __init fork_init(void)
cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
NULL, free_vm_stack_cache);
#endif
+
+ lockdep_init_task(&init_task);
}
int __weak arch_dup_task_struct(struct task_struct *dst,
@@ -1691,6 +1693,7 @@ static __latent_entropy struct task_struct *copy_process(
p->lockdep_depth = 0; /* no locks held yet */
p->curr_chain_key = 0;
p->lockdep_recursion = 0;
+ lockdep_init_task(p);
#endif
#ifdef CONFIG_DEBUG_MUTEXES
@@ -1949,6 +1952,7 @@ static __latent_entropy struct task_struct *copy_process(
bad_fork_cleanup_perf:
perf_event_free_task(p);
bad_fork_cleanup_policy:
+ lockdep_free_task(p);
#ifdef CONFIG_NUMA
mpol_put(p->mempolicy);
bad_fork_cleanup_threadgroup_lock:
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 22a13f9..afd6e64 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -58,6 +58,10 @@
#define CREATE_TRACE_POINTS
#include <trace/events/lock.h>
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+#include <linux/slab.h>
+#endif
+
#ifdef CONFIG_PROVE_LOCKING
int prove_locking = 1;
module_param(prove_locking, int, 0644);
@@ -726,6 +730,18 @@ static int count_matching_names(struct lock_class *new_class)
return is_static || static_obj(lock->key) ? NULL : ERR_PTR(-EINVAL);
}
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+static void cross_init(struct lockdep_map *lock, int cross);
+static int cross_lock(struct lockdep_map *lock);
+static int lock_acquire_crosslock(struct held_lock *hlock);
+static int lock_release_crosslock(struct lockdep_map *lock);
+#else
+static inline void cross_init(struct lockdep_map *lock, int cross) {}
+static inline int cross_lock(struct lockdep_map *lock) { return 0; }
+static inline int lock_acquire_crosslock(struct held_lock *hlock) { return 2; }
+static inline int lock_release_crosslock(struct lockdep_map *lock) { return 2; }
+#endif
+
/*
* Register a lock's class in the hash-table, if the class is not present
* yet. Otherwise we look it up. We cache the result in the lock object
@@ -1784,6 +1800,9 @@ static inline void inc_chains(void)
if (nest)
return 2;
+ if (cross_lock(prev->instance))
+ continue;
+
return print_deadlock_bug(curr, prev, next);
}
return 1;
@@ -1937,30 +1956,36 @@ static inline void inc_chains(void)
int distance = curr->lockdep_depth - depth + 1;
hlock = curr->held_locks + depth - 1;
/*
- * Only non-recursive-read entries get new dependencies
- * added:
+ * Only non-crosslock entries get new dependencies added.
+ * Crosslock entries will be added by commit later:
*/
- if (hlock->read != 2 && hlock->check) {
- int ret = check_prev_add(curr, hlock, next,
- distance, &trace, save);
- if (!ret)
- return 0;
-
+ if (!cross_lock(hlock->instance)) {
/*
- * Stop saving stack_trace if save_trace() was
- * called at least once:
+ * Only non-recursive-read entries get new dependencies
+ * added:
*/
- if (save && ret == 2)
- save = NULL;
+ if (hlock->read != 2 && hlock->check) {
+ int ret = check_prev_add(curr, hlock, next,
+ distance, &trace, save);
+ if (!ret)
+ return 0;
- /*
- * Stop after the first non-trylock entry,
- * as non-trylock entries have added their
- * own direct dependencies already, so this
- * lock is connected to them indirectly:
- */
- if (!hlock->trylock)
- break;
+ /*
+ * Stop saving stack_trace if save_trace() was
+ * called at least once:
+ */
+ if (save && ret == 2)
+ save = NULL;
+
+ /*
+ * Stop after the first non-trylock entry,
+ * as non-trylock entries have added their
+ * own direct dependencies already, so this
+ * lock is connected to them indirectly:
+ */
+ if (!hlock->trylock)
+ break;
+ }
}
depth--;
/*
@@ -3225,7 +3250,7 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
/*
* Initialize a lock instance's lock-class mapping info:
*/
-void lockdep_init_map(struct lockdep_map *lock, const char *name,
+static void __lockdep_init_map(struct lockdep_map *lock, const char *name,
struct lock_class_key *key, int subclass)
{
int i;
@@ -3283,8 +3308,25 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
raw_local_irq_restore(flags);
}
}
+
+void lockdep_init_map(struct lockdep_map *lock, const char *name,
+ struct lock_class_key *key, int subclass)
+{
+ cross_init(lock, 0);
+ __lockdep_init_map(lock, name, key, subclass);
+}
EXPORT_SYMBOL_GPL(lockdep_init_map);
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+void lockdep_init_map_crosslock(struct lockdep_map *lock, const char *name,
+ struct lock_class_key *key, int subclass)
+{
+ cross_init(lock, 1);
+ __lockdep_init_map(lock, name, key, subclass);
+}
+EXPORT_SYMBOL_GPL(lockdep_init_map_crosslock);
+#endif
+
struct lock_class_key __lockdep_no_validate__;
EXPORT_SYMBOL_GPL(__lockdep_no_validate__);
@@ -3340,6 +3382,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
int chain_head = 0;
int class_idx;
u64 chain_key;
+ int ret;
if (unlikely(!debug_locks))
return 0;
@@ -3388,7 +3431,8 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
class_idx = class - lock_classes + 1;
- if (depth) {
+ /* TODO: nest_lock is not implemented for crosslock yet. */
+ if (depth && !cross_lock(lock)) {
hlock = curr->held_locks + depth - 1;
if (hlock->class_idx == class_idx && nest_lock) {
if (hlock->references) {
@@ -3476,6 +3520,14 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
if (!validate_chain(curr, lock, hlock, chain_head, chain_key))
return 0;
+ ret = lock_acquire_crosslock(hlock);
+ /*
+ * 2 means normal acquire operations are needed. Otherwise, it's
+ * ok just to return with '0:fail, 1:success'.
+ */
+ if (ret != 2)
+ return ret;
+
curr->curr_chain_key = chain_key;
curr->lockdep_depth++;
check_chain_key(curr);
@@ -3713,11 +3765,19 @@ static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
struct task_struct *curr = current;
struct held_lock *hlock;
unsigned int depth;
- int i;
+ int ret, i;
if (unlikely(!debug_locks))
return 0;
+ ret = lock_release_crosslock(lock);
+ /*
+ * 2 means normal release operations are needed. Otherwise, it's
+ * ok just to return with '0:fail, 1:success'.
+ */
+ if (ret != 2)
+ return ret;
+
depth = curr->lockdep_depth;
/*
* So we're all set to release this lock.. wait what lock? We don't
@@ -4593,6 +4653,13 @@ asmlinkage __visible void lockdep_sys_exit(void)
curr->comm, curr->pid);
lockdep_print_held_locks(curr);
}
+
+ /*
+ * The lock history for each syscall should be independent. So wipe the
+ * slate clean on return to userspace.
+ */
+ crossrelease_hist_end(PROC);
+ crossrelease_hist_start(PROC);
}
void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
@@ -4641,3 +4708,398 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
dump_stack();
}
EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);
+
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+
+/*
+ * Crossrelease works by recording a lock history for each thread and
+ * connecting those historic locks that were taken after the
+ * wait_for_completion() in the complete() context.
+ *
+ * Task-A Task-B
+ *
+ * mutex_lock(&A);
+ * mutex_unlock(&A);
+ *
+ * wait_for_completion(&C);
+ * lock_acquire_crosslock();
+ * atomic_inc_return(&cross_gen_id);
+ * |
+ * | mutex_lock(&B);
+ * | mutex_unlock(&B);
+ * |
+ * | complete(&C);
+ * `-- lock_commit_crosslock();
+ *
+ * Which will then add a dependency between B and C.
+ */
+
+#define xhlock(i) (current->xhlocks[(i) % MAX_XHLOCKS_NR])
+
+/*
+ * Whenever a crosslock is held, cross_gen_id will be increased.
+ */
+static atomic_t cross_gen_id; /* Can be wrapped */
+
+/*
+ * Lock history stacks; we have 3 nested lock history stacks:
+ *
+ * Hard IRQ
+ * Soft IRQ
+ * History / Task
+ *
+ * The thing is that once we complete a (Hard/Soft) IRQ the future task locks
+ * should not depend on any of the locks observed while running the IRQ.
+ *
+ * So what we do is rewind the history buffer and erase all our knowledge of
+ * that temporal event.
+ */
+
+/*
+ * We need this to annotate lock history boundaries. Take for instance
+ * workqueues; each work is independent of the last. The completion of a future
+ * work does not depend on the completion of a past work (in general).
+ * Therefore we must not carry that (lock) dependency across works.
+ *
+ * This is true for many things; pretty much all kthreads fall into this
+ * pattern, where they have an 'idle' state and future completions do not
+ * depend on past completions. Its just that since they all have the 'same'
+ * form -- the kthread does the same over and over -- it doesn't typically
+ * matter.
+ *
+ * The same is true for system-calls, once a system call is completed (we've
+ * returned to userspace) the next system call does not depend on the lock
+ * history of the previous system call.
+ */
+void crossrelease_hist_start(enum context_t c)
+{
+ if (current->xhlocks)
+ current->xhlock_idx_hist[c] = current->xhlock_idx;
+}
+
+void crossrelease_hist_end(enum context_t c)
+{
+ if (current->xhlocks)
+ current->xhlock_idx = current->xhlock_idx_hist[c];
+}
+
+static int cross_lock(struct lockdep_map *lock)
+{
+ return lock ? lock->cross : 0;
+}
+
+/*
+ * This is needed to decide the relationship between wrapable variables.
+ */
+static inline int before(unsigned int a, unsigned int b)
+{
+ return (int)(a - b) < 0;
+}
+
+static inline struct lock_class *xhlock_class(struct hist_lock *xhlock)
+{
+ return hlock_class(&xhlock->hlock);
+}
+
+static inline struct lock_class *xlock_class(struct cross_lock *xlock)
+{
+ return hlock_class(&xlock->hlock);
+}
+
+/*
+ * Should we check a dependency with previous one?
+ */
+static inline int depend_before(struct held_lock *hlock)
+{
+ return hlock->read != 2 && hlock->check && !hlock->trylock;
+}
+
+/*
+ * Should we check a dependency with next one?
+ */
+static inline int depend_after(struct held_lock *hlock)
+{
+ return hlock->read != 2 && hlock->check;
+}
+
+/*
+ * Check if the xhlock is valid, which would be false if,
+ *
+ * 1. Has not used after initializaion yet.
+ *
+ * Remind hist_lock is implemented as a ring buffer.
+ */
+static inline int xhlock_valid(struct hist_lock *xhlock)
+{
+ /*
+ * xhlock->hlock.instance must be !NULL.
+ */
+ return !!xhlock->hlock.instance;
+}
+
+/*
+ * Record a hist_lock entry.
+ *
+ * Irq disable is only required.
+ */
+static void add_xhlock(struct held_lock *hlock)
+{
+ unsigned int idx = ++current->xhlock_idx;
+ struct hist_lock *xhlock = &xhlock(idx);
+
+#ifdef CONFIG_DEBUG_LOCKDEP
+ /*
+ * This can be done locklessly because they are all task-local
+ * state, we must however ensure IRQs are disabled.
+ */
+ WARN_ON_ONCE(!irqs_disabled());
+#endif
+
+ /* Initialize hist_lock's members */
+ xhlock->hlock = *hlock;
+
+ xhlock->trace.nr_entries = 0;
+ xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES;
+ xhlock->trace.entries = xhlock->trace_entries;
+ xhlock->trace.skip = 3;
+ save_stack_trace(&xhlock->trace);
+}
+
+static inline int same_context_xhlock(struct hist_lock *xhlock)
+{
+ return xhlock->hlock.irq_context == task_irq_context(current);
+}
+
+/*
+ * This should be lockless as far as possible because this would be
+ * called very frequently.
+ */
+static void check_add_xhlock(struct held_lock *hlock)
+{
+ /*
+ * Record a hist_lock, only in case that acquisitions ahead
+ * could depend on the held_lock. For example, if the held_lock
+ * is trylock then acquisitions ahead never depends on that.
+ * In that case, we don't need to record it. Just return.
+ */
+ if (!current->xhlocks || !depend_before(hlock))
+ return;
+
+ add_xhlock(hlock);
+}
+
+/*
+ * For crosslock.
+ */
+static int add_xlock(struct held_lock *hlock)
+{
+ struct cross_lock *xlock;
+ unsigned int gen_id;
+
+ if (!graph_lock())
+ return 0;
+
+ xlock = &((struct lockdep_map_cross *)hlock->instance)->xlock;
+
+ gen_id = (unsigned int)atomic_inc_return(&cross_gen_id);
+ xlock->hlock = *hlock;
+ xlock->hlock.gen_id = gen_id;
+ graph_unlock();
+
+ return 1;
+}
+
+/*
+ * Called for both normal and crosslock acquires. Normal locks will be
+ * pushed on the hist_lock queue. Cross locks will record state and
+ * stop regular lock_acquire() to avoid being placed on the held_lock
+ * stack.
+ *
+ * Return: 0 - failure;
+ * 1 - crosslock, done;
+ * 2 - normal lock, continue to held_lock[] ops.
+ */
+static int lock_acquire_crosslock(struct held_lock *hlock)
+{
+ /*
+ * CONTEXT 1 CONTEXT 2
+ * --------- ---------
+ * lock A (cross)
+ * X = atomic_inc_return(&cross_gen_id)
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ * Y = atomic_read_acquire(&cross_gen_id)
+ * lock B
+ *
+ * atomic_read_acquire() is for ordering between A and B,
+ * IOW, A happens before B, when CONTEXT 2 see Y >= X.
+ *
+ * Pairs with atomic_inc_return() in add_xlock().
+ */
+ hlock->gen_id = (unsigned int)atomic_read_acquire(&cross_gen_id);
+
+ if (cross_lock(hlock->instance))
+ return add_xlock(hlock);
+
+ check_add_xhlock(hlock);
+ return 2;
+}
+
+static int copy_trace(struct stack_trace *trace)
+{
+ unsigned long *buf = stack_trace + nr_stack_trace_entries;
+ unsigned int max_nr = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
+ unsigned int nr = min(max_nr, trace->nr_entries);
+
+ trace->nr_entries = nr;
+ memcpy(buf, trace->entries, nr * sizeof(trace->entries[0]));
+ trace->entries = buf;
+ nr_stack_trace_entries += nr;
+
+ if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES-1) {
+ if (!debug_locks_off_graph_unlock())
+ return 0;
+
+ print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!");
+ dump_stack();
+
+ return 0;
+ }
+
+ return 1;
+}
+
+static int commit_xhlock(struct cross_lock *xlock, struct hist_lock *xhlock)
+{
+ unsigned int xid, pid;
+ u64 chain_key;
+
+ xid = xlock_class(xlock) - lock_classes;
+ chain_key = iterate_chain_key((u64)0, xid);
+ pid = xhlock_class(xhlock) - lock_classes;
+ chain_key = iterate_chain_key(chain_key, pid);
+
+ if (lookup_chain_cache(chain_key))
+ return 1;
+
+ if (!add_chain_cache_classes(xid, pid, xhlock->hlock.irq_context,
+ chain_key))
+ return 0;
+
+ if (!check_prev_add(current, &xlock->hlock, &xhlock->hlock, 1,
+ &xhlock->trace, copy_trace))
+ return 0;
+
+ return 1;
+}
+
+static void commit_xhlocks(struct cross_lock *xlock)
+{
+ unsigned int cur = current->xhlock_idx;
+ unsigned int i;
+
+ if (!graph_lock())
+ return;
+
+ for (i = 0; i < MAX_XHLOCKS_NR; i++) {
+ struct hist_lock *xhlock = &xhlock(cur - i);
+
+ if (!xhlock_valid(xhlock))
+ break;
+
+ if (before(xhlock->hlock.gen_id, xlock->hlock.gen_id))
+ break;
+
+ if (!same_context_xhlock(xhlock))
+ break;
+
+ /*
+ * commit_xhlock() returns 0 with graph_lock already
+ * released if fail.
+ */
+ if (!commit_xhlock(xlock, xhlock))
+ return;
+ }
+
+ graph_unlock();
+}
+
+void lock_commit_crosslock(struct lockdep_map *lock)
+{
+ struct cross_lock *xlock;
+ unsigned long flags;
+
+ if (unlikely(!debug_locks || current->lockdep_recursion))
+ return;
+
+ if (!current->xhlocks)
+ return;
+
+ /*
+ * Do commit hist_locks with the cross_lock, only in case that
+ * the cross_lock could depend on acquisitions after that.
+ *
+ * For example, if the cross_lock does not have the 'check' flag
+ * then we don't need to check dependencies and commit for that.
+ * Just skip it. In that case, of course, the cross_lock does
+ * not depend on acquisitions ahead, either.
+ *
+ * WARNING: Don't do that in add_xlock() in advance. When an
+ * acquisition context is different from the commit context,
+ * invalid(skipped) cross_lock might be accessed.
+ */
+ if (!depend_after(&((struct lockdep_map_cross *)lock)->xlock.hlock))
+ return;
+
+ raw_local_irq_save(flags);
+ check_flags(flags);
+ current->lockdep_recursion = 1;
+ xlock = &((struct lockdep_map_cross *)lock)->xlock;
+ commit_xhlocks(xlock);
+ current->lockdep_recursion = 0;
+ raw_local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(lock_commit_crosslock);
+
+/*
+ * Return: 1 - crosslock, done;
+ * 2 - normal lock, continue to held_lock[] ops.
+ */
+static int lock_release_crosslock(struct lockdep_map *lock)
+{
+ return cross_lock(lock) ? 1 : 2;
+}
+
+static void cross_init(struct lockdep_map *lock, int cross)
+{
+ lock->cross = cross;
+
+ /*
+ * Crossrelease assumes that the ring buffer size of xhlocks
+ * is aligned with power of 2. So force it on build.
+ */
+ BUILD_BUG_ON(MAX_XHLOCKS_NR & (MAX_XHLOCKS_NR - 1));
+}
+
+void lockdep_init_task(struct task_struct *task)
+{
+ int i;
+
+ task->xhlock_idx = UINT_MAX;
+
+ for (i = 0; i < CONTEXT_NR; i++)
+ task->xhlock_idx_hist[i] = UINT_MAX;
+
+ task->xhlocks = kzalloc(sizeof(struct hist_lock) * MAX_XHLOCKS_NR,
+ GFP_KERNEL);
+}
+
+void lockdep_free_task(struct task_struct *task)
+{
+ if (task->xhlocks) {
+ void *tmp = task->xhlocks;
+ /* Diable crossrelease for current */
+ task->xhlocks = NULL;
+ kfree(tmp);
+ }
+}
+#endif
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a86688f..eb03c4f 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2093,6 +2093,7 @@ static void process_one_work(struct worker *worker, struct work_struct *work)
lock_map_acquire_read(&pwq->wq->lockdep_map);
lock_map_acquire(&lockdep_map);
+ crossrelease_hist_start(PROC);
trace_workqueue_execute_start(work);
worker->current_func(work);
/*
@@ -2100,6 +2101,7 @@ static void process_one_work(struct worker *worker, struct work_struct *work)
* point will only record its address.
*/
trace_workqueue_execute_end(work);
+ crossrelease_hist_end(PROC);
lock_map_release(&lockdep_map);
lock_map_release(&pwq->wq->lockdep_map);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 98fe715..037e813 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1073,6 +1073,18 @@ config DEBUG_LOCK_ALLOC
spin_lock_init()/mutex_init()/etc., or whether there is any lock
held during task exit.
+config LOCKDEP_CROSSRELEASE
+ bool "Lock debugging: make lockdep work for crosslocks"
+ depends on PROVE_LOCKING
+ default n
+ help
+ This makes lockdep work for crosslock which is a lock allowed to
+ be released in a different context from the acquisition context.
+ Normally a lock must be released in the context acquiring the lock.
+ However, relexing this constraint helps synchronization primitives
+ such as page locks or completions can use the lock correctness
+ detector, lockdep.
+
config PROVE_LOCKING
bool "Lock debugging: prove locking correctness"
depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
--
1.9.1
[toc] | [prev] | [next] | [standalone]
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Date | 2017-08-09 16:10 +0200 |
| Subject | Re: [PATCH v8 05/14] lockdep: Implement crossrelease feature |
| Message-ID | <uczQl-8qK-3@gated-at.bofh.it> |
| In reply to | #1705153 |
On Mon, Aug 07, 2017 at 04:12:52PM +0900, Byungchul Park wrote:
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index fffe49f..0c8a1b8 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -467,6 +520,49 @@ static inline void lockdep_on(void)
>
> #endif /* !LOCKDEP */
>
> +enum context_t {
> + HARD,
> + SOFT,
> + PROC,
> + CONTEXT_NR,
> +};
Since this is the global namespace and those being somewhat generic
names, I've renamed the lot:
+enum xhlock_context_t {
+ XHLOCK_HARD,
+ XHLOCK_SOFT,
+ XHLOCK_PROC,
+ XHLOCK_NR,
+};
[toc] | [prev] | [next] | [standalone]
| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-10 03:40 +0200 |
| Subject | Re: [PATCH v8 05/14] lockdep: Implement crossrelease feature |
| Message-ID | <ucKC6-79t-15@gated-at.bofh.it> |
| In reply to | #1707358 |
On Wed, Aug 09, 2017 at 04:05:35PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 07, 2017 at 04:12:52PM +0900, Byungchul Park wrote:
> > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> > index fffe49f..0c8a1b8 100644
> > --- a/include/linux/lockdep.h
> > +++ b/include/linux/lockdep.h
> > @@ -467,6 +520,49 @@ static inline void lockdep_on(void)
> >
> > #endif /* !LOCKDEP */
> >
> > +enum context_t {
> > + HARD,
> > + SOFT,
> > + PROC,
> > + CONTEXT_NR,
> > +};
>
> Since this is the global namespace and those being somewhat generic
> names, I've renamed the lot:
>
> +enum xhlock_context_t {
> + XHLOCK_HARD,
> + XHLOCK_SOFT,
> + XHLOCK_PROC,
> + XHLOCK_NR,
> +};
I like it. Thank you.
With a little feedback, it rather makes us a bit confused between
XHLOCK_NR and MAX_XHLOCK_NR. what about the following?
+enum xhlock_context_t {
+ XHLOCK_HARD,
+ XHLOCK_SOFT,
+ XHLOCK_PROC,
+ XHLOCK_CXT_NR,
+};
But it's trivial. I like yours, too.
[toc] | [prev] | [next] | [standalone]
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Date | 2017-08-10 11:30 +0200 |
| Subject | Re: [PATCH v8 05/14] lockdep: Implement crossrelease feature |
| Message-ID | <ucRWV-3Ia-1@gated-at.bofh.it> |
| In reply to | #1708131 |
On Thu, Aug 10, 2017 at 10:30:54AM +0900, Byungchul Park wrote:
> With a little feedback, it rather makes us a bit confused between
> XHLOCK_NR and MAX_XHLOCK_NR. what about the following?
>
> +enum xhlock_context_t {
> + XHLOCK_HARD,
> + XHLOCK_SOFT,
> + XHLOCK_PROC,
> + XHLOCK_CXT_NR,
> +};
>
> But it's trivial. I like yours, too.
grep -l "XHLOCK_NR" `quilt series` | while read file; do sed -i
's/XHLOCK_NR/XHLOCK_CTX_NR/g' $file; done
:-)
[toc] | [prev] | [next] | [standalone]
| From | tip-bot for Byungchul Park <tipbot@zytor.com> |
|---|---|
| Date | 2017-08-10 14:30 +0200 |
| Subject | [tip:locking/core] locking/lockdep: Implement the 'crossrelease' feature |
| Message-ID | <ucUL8-5wC-11@gated-at.bofh.it> |
| In reply to | #1705153 |
Commit-ID: b09be676e0ff25bd6d2e7637e26d349f9109ad75
Gitweb: http://git.kernel.org/tip/b09be676e0ff25bd6d2e7637e26d349f9109ad75
Author: Byungchul Park <byungchul.park@lge.com>
AuthorDate: Mon, 7 Aug 2017 16:12:52 +0900
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 10 Aug 2017 12:29:07 +0200
locking/lockdep: Implement the 'crossrelease' feature
Lockdep is a runtime locking correctness validator that detects and
reports a deadlock or its possibility by checking dependencies between
locks. It's useful since it does not report just an actual deadlock but
also the possibility of a deadlock that has not actually happened yet.
That enables problems to be fixed before they affect real systems.
However, this facility is only applicable to typical locks, such as
spinlocks and mutexes, which are normally released within the context in
which they were acquired. However, synchronization primitives like page
locks or completions, which are allowed to be released in any context,
also create dependencies and can cause a deadlock.
So lockdep should track these locks to do a better job. The 'crossrelease'
implementation makes these primitives also be tracked.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akpm@linux-foundation.org
Cc: boqun.feng@gmail.com
Cc: kernel-team@lge.com
Cc: kirill@shutemov.name
Cc: npiggin@gmail.com
Cc: walken@google.com
Cc: willy@infradead.org
Link: http://lkml.kernel.org/r/1502089981-21272-6-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/linux/irqflags.h | 24 ++-
include/linux/lockdep.h | 110 +++++++++-
include/linux/sched.h | 8 +
kernel/exit.c | 1 +
kernel/fork.c | 4 +
kernel/locking/lockdep.c | 508 ++++++++++++++++++++++++++++++++++++++++++++---
kernel/workqueue.c | 2 +
lib/Kconfig.debug | 12 ++
8 files changed, 635 insertions(+), 34 deletions(-)
diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 5dd1272..5fdd93b 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -23,10 +23,26 @@
# define trace_softirq_context(p) ((p)->softirq_context)
# define trace_hardirqs_enabled(p) ((p)->hardirqs_enabled)
# define trace_softirqs_enabled(p) ((p)->softirqs_enabled)
-# define trace_hardirq_enter() do { current->hardirq_context++; } while (0)
-# define trace_hardirq_exit() do { current->hardirq_context--; } while (0)
-# define lockdep_softirq_enter() do { current->softirq_context++; } while (0)
-# define lockdep_softirq_exit() do { current->softirq_context--; } while (0)
+# define trace_hardirq_enter() \
+do { \
+ current->hardirq_context++; \
+ crossrelease_hist_start(XHLOCK_HARD); \
+} while (0)
+# define trace_hardirq_exit() \
+do { \
+ current->hardirq_context--; \
+ crossrelease_hist_end(XHLOCK_HARD); \
+} while (0)
+# define lockdep_softirq_enter() \
+do { \
+ current->softirq_context++; \
+ crossrelease_hist_start(XHLOCK_SOFT); \
+} while (0)
+# define lockdep_softirq_exit() \
+do { \
+ current->softirq_context--; \
+ crossrelease_hist_end(XHLOCK_SOFT); \
+} while (0)
# define INIT_TRACE_IRQFLAGS .softirqs_enabled = 1,
#else
# define trace_hardirqs_on() do { } while (0)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 0a4c02c..e1e0fcd 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -155,6 +155,12 @@ struct lockdep_map {
int cpu;
unsigned long ip;
#endif
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+ /*
+ * Whether it's a crosslock.
+ */
+ int cross;
+#endif
};
static inline void lockdep_copy_map(struct lockdep_map *to,
@@ -258,8 +264,62 @@ struct held_lock {
unsigned int hardirqs_off:1;
unsigned int references:12; /* 32 bits */
unsigned int pin_count;
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+ /*
+ * Generation id.
+ *
+ * A value of cross_gen_id will be stored when holding this,
+ * which is globally increased whenever each crosslock is held.
+ */
+ unsigned int gen_id;
+#endif
+};
+
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+#define MAX_XHLOCK_TRACE_ENTRIES 5
+
+/*
+ * This is for keeping locks waiting for commit so that true dependencies
+ * can be added at commit step.
+ */
+struct hist_lock {
+ /*
+ * Seperate stack_trace data. This will be used at commit step.
+ */
+ struct stack_trace trace;
+ unsigned long trace_entries[MAX_XHLOCK_TRACE_ENTRIES];
+
+ /*
+ * Seperate hlock instance. This will be used at commit step.
+ *
+ * TODO: Use a smaller data structure containing only necessary
+ * data. However, we should make lockdep code able to handle the
+ * smaller one first.
+ */
+ struct held_lock hlock;
+};
+
+/*
+ * To initialize a lock as crosslock, lockdep_init_map_crosslock() should
+ * be called instead of lockdep_init_map().
+ */
+struct cross_lock {
+ /*
+ * Seperate hlock instance. This will be used at commit step.
+ *
+ * TODO: Use a smaller data structure containing only necessary
+ * data. However, we should make lockdep code able to handle the
+ * smaller one first.
+ */
+ struct held_lock hlock;
};
+struct lockdep_map_cross {
+ struct lockdep_map map;
+ struct cross_lock xlock;
+};
+#endif
+
/*
* Initialization, self-test and debugging-output methods:
*/
@@ -282,13 +342,6 @@ extern void lockdep_init_map(struct lockdep_map *lock, const char *name,
struct lock_class_key *key, int subclass);
/*
- * To initialize a lockdep_map statically use this macro.
- * Note that _name must not be NULL.
- */
-#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
- { .name = (_name), .key = (void *)(_key), }
-
-/*
* Reinitialize a lock key - for cases where there is special locking or
* special initialization of locks so that the validator gets the scope
* of dependencies wrong: they are either too broad (they need a class-split)
@@ -460,6 +513,49 @@ struct pin_cookie { };
#endif /* !LOCKDEP */
+enum xhlock_context_t {
+ XHLOCK_HARD,
+ XHLOCK_SOFT,
+ XHLOCK_PROC,
+ XHLOCK_CTX_NR,
+};
+
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+extern void lockdep_init_map_crosslock(struct lockdep_map *lock,
+ const char *name,
+ struct lock_class_key *key,
+ int subclass);
+extern void lock_commit_crosslock(struct lockdep_map *lock);
+
+#define STATIC_CROSS_LOCKDEP_MAP_INIT(_name, _key) \
+ { .map.name = (_name), .map.key = (void *)(_key), \
+ .map.cross = 1, }
+
+/*
+ * To initialize a lockdep_map statically use this macro.
+ * Note that _name must not be NULL.
+ */
+#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
+ { .name = (_name), .key = (void *)(_key), .cross = 0, }
+
+extern void crossrelease_hist_start(enum xhlock_context_t c);
+extern void crossrelease_hist_end(enum xhlock_context_t c);
+extern void lockdep_init_task(struct task_struct *task);
+extern void lockdep_free_task(struct task_struct *task);
+#else
+/*
+ * To initialize a lockdep_map statically use this macro.
+ * Note that _name must not be NULL.
+ */
+#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
+ { .name = (_name), .key = (void *)(_key), }
+
+static inline void crossrelease_hist_start(enum xhlock_context_t c) {}
+static inline void crossrelease_hist_end(enum xhlock_context_t c) {}
+static inline void lockdep_init_task(struct task_struct *task) {}
+static inline void lockdep_free_task(struct task_struct *task) {}
+#endif
+
#ifdef CONFIG_LOCK_STAT
extern void lock_contended(struct lockdep_map *lock, unsigned long ip);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 57db70e..5235fba 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -848,6 +848,14 @@ struct task_struct {
struct held_lock held_locks[MAX_LOCK_DEPTH];
#endif
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+#define MAX_XHLOCKS_NR 64UL
+ struct hist_lock *xhlocks; /* Crossrelease history locks */
+ unsigned int xhlock_idx;
+ /* For restoring at history boundaries */
+ unsigned int xhlock_idx_hist[XHLOCK_CTX_NR];
+#endif
+
#ifdef CONFIG_UBSAN
unsigned int in_ubsan;
#endif
diff --git a/kernel/exit.c b/kernel/exit.c
index c5548fa..fa72d57 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -920,6 +920,7 @@ void __noreturn do_exit(long code)
exit_rcu();
TASKS_RCU(__srcu_read_unlock(&tasks_rcu_exit_srcu, tasks_rcu_i));
+ lockdep_free_task(tsk);
do_task_dead();
}
EXPORT_SYMBOL_GPL(do_exit);
diff --git a/kernel/fork.c b/kernel/fork.c
index 17921b0..cbf2221 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -484,6 +484,8 @@ void __init fork_init(void)
cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
NULL, free_vm_stack_cache);
#endif
+
+ lockdep_init_task(&init_task);
}
int __weak arch_dup_task_struct(struct task_struct *dst,
@@ -1691,6 +1693,7 @@ static __latent_entropy struct task_struct *copy_process(
p->lockdep_depth = 0; /* no locks held yet */
p->curr_chain_key = 0;
p->lockdep_recursion = 0;
+ lockdep_init_task(p);
#endif
#ifdef CONFIG_DEBUG_MUTEXES
@@ -1949,6 +1952,7 @@ bad_fork_cleanup_audit:
bad_fork_cleanup_perf:
perf_event_free_task(p);
bad_fork_cleanup_policy:
+ lockdep_free_task(p);
#ifdef CONFIG_NUMA
mpol_put(p->mempolicy);
bad_fork_cleanup_threadgroup_lock:
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 841828b..56f69cc 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -58,6 +58,10 @@
#define CREATE_TRACE_POINTS
#include <trace/events/lock.h>
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+#include <linux/slab.h>
+#endif
+
#ifdef CONFIG_PROVE_LOCKING
int prove_locking = 1;
module_param(prove_locking, int, 0644);
@@ -724,6 +728,18 @@ look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
return is_static || static_obj(lock->key) ? NULL : ERR_PTR(-EINVAL);
}
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+static void cross_init(struct lockdep_map *lock, int cross);
+static int cross_lock(struct lockdep_map *lock);
+static int lock_acquire_crosslock(struct held_lock *hlock);
+static int lock_release_crosslock(struct lockdep_map *lock);
+#else
+static inline void cross_init(struct lockdep_map *lock, int cross) {}
+static inline int cross_lock(struct lockdep_map *lock) { return 0; }
+static inline int lock_acquire_crosslock(struct held_lock *hlock) { return 2; }
+static inline int lock_release_crosslock(struct lockdep_map *lock) { return 2; }
+#endif
+
/*
* Register a lock's class in the hash-table, if the class is not present
* yet. Otherwise we look it up. We cache the result in the lock object
@@ -1795,6 +1811,9 @@ check_deadlock(struct task_struct *curr, struct held_lock *next,
if (nest)
return 2;
+ if (cross_lock(prev->instance))
+ continue;
+
return print_deadlock_bug(curr, prev, next);
}
return 1;
@@ -1962,30 +1981,36 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
int distance = curr->lockdep_depth - depth + 1;
hlock = curr->held_locks + depth - 1;
/*
- * Only non-recursive-read entries get new dependencies
- * added:
+ * Only non-crosslock entries get new dependencies added.
+ * Crosslock entries will be added by commit later:
*/
- if (hlock->read != 2 && hlock->check) {
- int ret = check_prev_add(curr, hlock, next,
- distance, &trace, save);
- if (!ret)
- return 0;
-
+ if (!cross_lock(hlock->instance)) {
/*
- * Stop saving stack_trace if save_trace() was
- * called at least once:
+ * Only non-recursive-read entries get new dependencies
+ * added:
*/
- if (save && ret == 2)
- save = NULL;
+ if (hlock->read != 2 && hlock->check) {
+ int ret = check_prev_add(curr, hlock, next,
+ distance, &trace, save);
+ if (!ret)
+ return 0;
- /*
- * Stop after the first non-trylock entry,
- * as non-trylock entries have added their
- * own direct dependencies already, so this
- * lock is connected to them indirectly:
- */
- if (!hlock->trylock)
- break;
+ /*
+ * Stop saving stack_trace if save_trace() was
+ * called at least once:
+ */
+ if (save && ret == 2)
+ save = NULL;
+
+ /*
+ * Stop after the first non-trylock entry,
+ * as non-trylock entries have added their
+ * own direct dependencies already, so this
+ * lock is connected to them indirectly:
+ */
+ if (!hlock->trylock)
+ break;
+ }
}
depth--;
/*
@@ -3176,7 +3201,7 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
/*
* Initialize a lock instance's lock-class mapping info:
*/
-void lockdep_init_map(struct lockdep_map *lock, const char *name,
+static void __lockdep_init_map(struct lockdep_map *lock, const char *name,
struct lock_class_key *key, int subclass)
{
int i;
@@ -3234,8 +3259,25 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
raw_local_irq_restore(flags);
}
}
+
+void lockdep_init_map(struct lockdep_map *lock, const char *name,
+ struct lock_class_key *key, int subclass)
+{
+ cross_init(lock, 0);
+ __lockdep_init_map(lock, name, key, subclass);
+}
EXPORT_SYMBOL_GPL(lockdep_init_map);
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+void lockdep_init_map_crosslock(struct lockdep_map *lock, const char *name,
+ struct lock_class_key *key, int subclass)
+{
+ cross_init(lock, 1);
+ __lockdep_init_map(lock, name, key, subclass);
+}
+EXPORT_SYMBOL_GPL(lockdep_init_map_crosslock);
+#endif
+
struct lock_class_key __lockdep_no_validate__;
EXPORT_SYMBOL_GPL(__lockdep_no_validate__);
@@ -3291,6 +3333,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
int chain_head = 0;
int class_idx;
u64 chain_key;
+ int ret;
if (unlikely(!debug_locks))
return 0;
@@ -3339,7 +3382,8 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
class_idx = class - lock_classes + 1;
- if (depth) {
+ /* TODO: nest_lock is not implemented for crosslock yet. */
+ if (depth && !cross_lock(lock)) {
hlock = curr->held_locks + depth - 1;
if (hlock->class_idx == class_idx && nest_lock) {
if (hlock->references) {
@@ -3427,6 +3471,14 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
if (!validate_chain(curr, lock, hlock, chain_head, chain_key))
return 0;
+ ret = lock_acquire_crosslock(hlock);
+ /*
+ * 2 means normal acquire operations are needed. Otherwise, it's
+ * ok just to return with '0:fail, 1:success'.
+ */
+ if (ret != 2)
+ return ret;
+
curr->curr_chain_key = chain_key;
curr->lockdep_depth++;
check_chain_key(curr);
@@ -3664,11 +3716,19 @@ __lock_release(struct lockdep_map *lock, int nested, unsigned long ip)
struct task_struct *curr = current;
struct held_lock *hlock;
unsigned int depth;
- int i;
+ int ret, i;
if (unlikely(!debug_locks))
return 0;
+ ret = lock_release_crosslock(lock);
+ /*
+ * 2 means normal release operations are needed. Otherwise, it's
+ * ok just to return with '0:fail, 1:success'.
+ */
+ if (ret != 2)
+ return ret;
+
depth = curr->lockdep_depth;
/*
* So we're all set to release this lock.. wait what lock? We don't
@@ -4532,6 +4592,13 @@ asmlinkage __visible void lockdep_sys_exit(void)
curr->comm, curr->pid);
lockdep_print_held_locks(curr);
}
+
+ /*
+ * The lock history for each syscall should be independent. So wipe the
+ * slate clean on return to userspace.
+ */
+ crossrelease_hist_end(XHLOCK_PROC);
+ crossrelease_hist_start(XHLOCK_PROC);
}
void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
@@ -4580,3 +4647,398 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
dump_stack();
}
EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);
+
+#ifdef CONFIG_LOCKDEP_CROSSRELEASE
+
+/*
+ * Crossrelease works by recording a lock history for each thread and
+ * connecting those historic locks that were taken after the
+ * wait_for_completion() in the complete() context.
+ *
+ * Task-A Task-B
+ *
+ * mutex_lock(&A);
+ * mutex_unlock(&A);
+ *
+ * wait_for_completion(&C);
+ * lock_acquire_crosslock();
+ * atomic_inc_return(&cross_gen_id);
+ * |
+ * | mutex_lock(&B);
+ * | mutex_unlock(&B);
+ * |
+ * | complete(&C);
+ * `-- lock_commit_crosslock();
+ *
+ * Which will then add a dependency between B and C.
+ */
+
+#define xhlock(i) (current->xhlocks[(i) % MAX_XHLOCKS_NR])
+
+/*
+ * Whenever a crosslock is held, cross_gen_id will be increased.
+ */
+static atomic_t cross_gen_id; /* Can be wrapped */
+
+/*
+ * Lock history stacks; we have 3 nested lock history stacks:
+ *
+ * Hard IRQ
+ * Soft IRQ
+ * History / Task
+ *
+ * The thing is that once we complete a (Hard/Soft) IRQ the future task locks
+ * should not depend on any of the locks observed while running the IRQ.
+ *
+ * So what we do is rewind the history buffer and erase all our knowledge of
+ * that temporal event.
+ */
+
+/*
+ * We need this to annotate lock history boundaries. Take for instance
+ * workqueues; each work is independent of the last. The completion of a future
+ * work does not depend on the completion of a past work (in general).
+ * Therefore we must not carry that (lock) dependency across works.
+ *
+ * This is true for many things; pretty much all kthreads fall into this
+ * pattern, where they have an 'idle' state and future completions do not
+ * depend on past completions. Its just that since they all have the 'same'
+ * form -- the kthread does the same over and over -- it doesn't typically
+ * matter.
+ *
+ * The same is true for system-calls, once a system call is completed (we've
+ * returned to userspace) the next system call does not depend on the lock
+ * history of the previous system call.
+ */
+void crossrelease_hist_start(enum xhlock_context_t c)
+{
+ if (current->xhlocks)
+ current->xhlock_idx_hist[c] = current->xhlock_idx;
+}
+
+void crossrelease_hist_end(enum xhlock_context_t c)
+{
+ if (current->xhlocks)
+ current->xhlock_idx = current->xhlock_idx_hist[c];
+}
+
+static int cross_lock(struct lockdep_map *lock)
+{
+ return lock ? lock->cross : 0;
+}
+
+/*
+ * This is needed to decide the relationship between wrapable variables.
+ */
+static inline int before(unsigned int a, unsigned int b)
+{
+ return (int)(a - b) < 0;
+}
+
+static inline struct lock_class *xhlock_class(struct hist_lock *xhlock)
+{
+ return hlock_class(&xhlock->hlock);
+}
+
+static inline struct lock_class *xlock_class(struct cross_lock *xlock)
+{
+ return hlock_class(&xlock->hlock);
+}
+
+/*
+ * Should we check a dependency with previous one?
+ */
+static inline int depend_before(struct held_lock *hlock)
+{
+ return hlock->read != 2 && hlock->check && !hlock->trylock;
+}
+
+/*
+ * Should we check a dependency with next one?
+ */
+static inline int depend_after(struct held_lock *hlock)
+{
+ return hlock->read != 2 && hlock->check;
+}
+
+/*
+ * Check if the xhlock is valid, which would be false if,
+ *
+ * 1. Has not used after initializaion yet.
+ *
+ * Remind hist_lock is implemented as a ring buffer.
+ */
+static inline int xhlock_valid(struct hist_lock *xhlock)
+{
+ /*
+ * xhlock->hlock.instance must be !NULL.
+ */
+ return !!xhlock->hlock.instance;
+}
+
+/*
+ * Record a hist_lock entry.
+ *
+ * Irq disable is only required.
+ */
+static void add_xhlock(struct held_lock *hlock)
+{
+ unsigned int idx = ++current->xhlock_idx;
+ struct hist_lock *xhlock = &xhlock(idx);
+
+#ifdef CONFIG_DEBUG_LOCKDEP
+ /*
+ * This can be done locklessly because they are all task-local
+ * state, we must however ensure IRQs are disabled.
+ */
+ WARN_ON_ONCE(!irqs_disabled());
+#endif
+
+ /* Initialize hist_lock's members */
+ xhlock->hlock = *hlock;
+
+ xhlock->trace.nr_entries = 0;
+ xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES;
+ xhlock->trace.entries = xhlock->trace_entries;
+ xhlock->trace.skip = 3;
+ save_stack_trace(&xhlock->trace);
+}
+
+static inline int same_context_xhlock(struct hist_lock *xhlock)
+{
+ return xhlock->hlock.irq_context == task_irq_context(current);
+}
+
+/*
+ * This should be lockless as far as possible because this would be
+ * called very frequently.
+ */
+static void check_add_xhlock(struct held_lock *hlock)
+{
+ /*
+ * Record a hist_lock, only in case that acquisitions ahead
+ * could depend on the held_lock. For example, if the held_lock
+ * is trylock then acquisitions ahead never depends on that.
+ * In that case, we don't need to record it. Just return.
+ */
+ if (!current->xhlocks || !depend_before(hlock))
+ return;
+
+ add_xhlock(hlock);
+}
+
+/*
+ * For crosslock.
+ */
+static int add_xlock(struct held_lock *hlock)
+{
+ struct cross_lock *xlock;
+ unsigned int gen_id;
+
+ if (!graph_lock())
+ return 0;
+
+ xlock = &((struct lockdep_map_cross *)hlock->instance)->xlock;
+
+ gen_id = (unsigned int)atomic_inc_return(&cross_gen_id);
+ xlock->hlock = *hlock;
+ xlock->hlock.gen_id = gen_id;
+ graph_unlock();
+
+ return 1;
+}
+
+/*
+ * Called for both normal and crosslock acquires. Normal locks will be
+ * pushed on the hist_lock queue. Cross locks will record state and
+ * stop regular lock_acquire() to avoid being placed on the held_lock
+ * stack.
+ *
+ * Return: 0 - failure;
+ * 1 - crosslock, done;
+ * 2 - normal lock, continue to held_lock[] ops.
+ */
+static int lock_acquire_crosslock(struct held_lock *hlock)
+{
+ /*
+ * CONTEXT 1 CONTEXT 2
+ * --------- ---------
+ * lock A (cross)
+ * X = atomic_inc_return(&cross_gen_id)
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ * Y = atomic_read_acquire(&cross_gen_id)
+ * lock B
+ *
+ * atomic_read_acquire() is for ordering between A and B,
+ * IOW, A happens before B, when CONTEXT 2 see Y >= X.
+ *
+ * Pairs with atomic_inc_return() in add_xlock().
+ */
+ hlock->gen_id = (unsigned int)atomic_read_acquire(&cross_gen_id);
+
+ if (cross_lock(hlock->instance))
+ return add_xlock(hlock);
+
+ check_add_xhlock(hlock);
+ return 2;
+}
+
+static int copy_trace(struct stack_trace *trace)
+{
+ unsigned long *buf = stack_trace + nr_stack_trace_entries;
+ unsigned int max_nr = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
+ unsigned int nr = min(max_nr, trace->nr_entries);
+
+ trace->nr_entries = nr;
+ memcpy(buf, trace->entries, nr * sizeof(trace->entries[0]));
+ trace->entries = buf;
+ nr_stack_trace_entries += nr;
+
+ if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES-1) {
+ if (!debug_locks_off_graph_unlock())
+ return 0;
+
+ print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!");
+ dump_stack();
+
+ return 0;
+ }
+
+ return 1;
+}
+
+static int commit_xhlock(struct cross_lock *xlock, struct hist_lock *xhlock)
+{
+ unsigned int xid, pid;
+ u64 chain_key;
+
+ xid = xlock_class(xlock) - lock_classes;
+ chain_key = iterate_chain_key((u64)0, xid);
+ pid = xhlock_class(xhlock) - lock_classes;
+ chain_key = iterate_chain_key(chain_key, pid);
+
+ if (lookup_chain_cache(chain_key))
+ return 1;
+
+ if (!add_chain_cache_classes(xid, pid, xhlock->hlock.irq_context,
+ chain_key))
+ return 0;
+
+ if (!check_prev_add(current, &xlock->hlock, &xhlock->hlock, 1,
+ &xhlock->trace, copy_trace))
+ return 0;
+
+ return 1;
+}
+
+static void commit_xhlocks(struct cross_lock *xlock)
+{
+ unsigned int cur = current->xhlock_idx;
+ unsigned int i;
+
+ if (!graph_lock())
+ return;
+
+ for (i = 0; i < MAX_XHLOCKS_NR; i++) {
+ struct hist_lock *xhlock = &xhlock(cur - i);
+
+ if (!xhlock_valid(xhlock))
+ break;
+
+ if (before(xhlock->hlock.gen_id, xlock->hlock.gen_id))
+ break;
+
+ if (!same_context_xhlock(xhlock))
+ break;
+
+ /*
+ * commit_xhlock() returns 0 with graph_lock already
+ * released if fail.
+ */
+ if (!commit_xhlock(xlock, xhlock))
+ return;
+ }
+
+ graph_unlock();
+}
+
+void lock_commit_crosslock(struct lockdep_map *lock)
+{
+ struct cross_lock *xlock;
+ unsigned long flags;
+
+ if (unlikely(!debug_locks || current->lockdep_recursion))
+ return;
+
+ if (!current->xhlocks)
+ return;
+
+ /*
+ * Do commit hist_locks with the cross_lock, only in case that
+ * the cross_lock could depend on acquisitions after that.
+ *
+ * For example, if the cross_lock does not have the 'check' flag
+ * then we don't need to check dependencies and commit for that.
+ * Just skip it. In that case, of course, the cross_lock does
+ * not depend on acquisitions ahead, either.
+ *
+ * WARNING: Don't do that in add_xlock() in advance. When an
+ * acquisition context is different from the commit context,
+ * invalid(skipped) cross_lock might be accessed.
+ */
+ if (!depend_after(&((struct lockdep_map_cross *)lock)->xlock.hlock))
+ return;
+
+ raw_local_irq_save(flags);
+ check_flags(flags);
+ current->lockdep_recursion = 1;
+ xlock = &((struct lockdep_map_cross *)lock)->xlock;
+ commit_xhlocks(xlock);
+ current->lockdep_recursion = 0;
+ raw_local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(lock_commit_crosslock);
+
+/*
+ * Return: 1 - crosslock, done;
+ * 2 - normal lock, continue to held_lock[] ops.
+ */
+static int lock_release_crosslock(struct lockdep_map *lock)
+{
+ return cross_lock(lock) ? 1 : 2;
+}
+
+static void cross_init(struct lockdep_map *lock, int cross)
+{
+ lock->cross = cross;
+
+ /*
+ * Crossrelease assumes that the ring buffer size of xhlocks
+ * is aligned with power of 2. So force it on build.
+ */
+ BUILD_BUG_ON(MAX_XHLOCKS_NR & (MAX_XHLOCKS_NR - 1));
+}
+
+void lockdep_init_task(struct task_struct *task)
+{
+ int i;
+
+ task->xhlock_idx = UINT_MAX;
+
+ for (i = 0; i < XHLOCK_CTX_NR; i++)
+ task->xhlock_idx_hist[i] = UINT_MAX;
+
+ task->xhlocks = kzalloc(sizeof(struct hist_lock) * MAX_XHLOCKS_NR,
+ GFP_KERNEL);
+}
+
+void lockdep_free_task(struct task_struct *task)
+{
+ if (task->xhlocks) {
+ void *tmp = task->xhlocks;
+ /* Diable crossrelease for current */
+ task->xhlocks = NULL;
+ kfree(tmp);
+ }
+}
+#endif
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ca937b0..e86733a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2093,6 +2093,7 @@ __acquires(&pool->lock)
lock_map_acquire_read(&pwq->wq->lockdep_map);
lock_map_acquire(&lockdep_map);
+ crossrelease_hist_start(XHLOCK_PROC);
trace_workqueue_execute_start(work);
worker->current_func(work);
/*
@@ -2100,6 +2101,7 @@ __acquires(&pool->lock)
* point will only record its address.
*/
trace_workqueue_execute_end(work);
+ crossrelease_hist_end(XHLOCK_PROC);
lock_map_release(&lockdep_map);
lock_map_release(&pwq->wq->lockdep_map);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 98fe715..c6038f2 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1150,6 +1150,18 @@ config LOCK_STAT
CONFIG_LOCK_STAT defines "contended" and "acquired" lock events.
(CONFIG_LOCKDEP defines "acquire" and "release" events.)
+config LOCKDEP_CROSSRELEASE
+ bool "Lock debugging: make lockdep work for crosslocks"
+ depends on PROVE_LOCKING
+ default n
+ help
+ This makes lockdep work for crosslock which is a lock allowed to
+ be released in a different context from the acquisition context.
+ Normally a lock must be released in the context acquiring the lock.
+ However, relexing this constraint helps synchronization primitives
+ such as page locks or completions can use the lock correctness
+ detector, lockdep.
+
config DEBUG_LOCKDEP
bool "Lock dependency engine debugging"
depends on DEBUG_KERNEL && LOCKDEP
[toc] | [prev] | [next] | [standalone]
| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-07 09:20 +0200 |
| Subject | [PATCH v8 11/14] lockdep: Apply crossrelease to PG_locked locks |
| Message-ID | <ubKuu-59V-27@gated-at.bofh.it> |
| In reply to | #1705149 |
Although lock_page() and its family can cause deadlock, the lock
correctness validator could not be applied to them until now, becasue
things like unlock_page() might be called in a different context from
the acquisition context, which violates lockdep's assumption.
Thanks to CONFIG_LOCKDEP_CROSSRELEASE, we can now apply the lockdep
detector to page locks. Applied it.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
include/linux/mm_types.h | 8 ++++
include/linux/pagemap.h | 101 ++++++++++++++++++++++++++++++++++++++++++++---
lib/Kconfig.debug | 8 ++++
mm/filemap.c | 4 +-
mm/page_alloc.c | 3 ++
5 files changed, 116 insertions(+), 8 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index ff15181..f1e3dba 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -16,6 +16,10 @@
#include <asm/mmu.h>
+#ifdef CONFIG_LOCKDEP_PAGELOCK
+#include <linux/lockdep.h>
+#endif
+
#ifndef AT_VECTOR_SIZE_ARCH
#define AT_VECTOR_SIZE_ARCH 0
#endif
@@ -216,6 +220,10 @@ struct page {
#ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
int _last_cpupid;
#endif
+
+#ifdef CONFIG_LOCKDEP_PAGELOCK
+ struct lockdep_map_cross map;
+#endif
}
/*
* The struct page can be forced to be double word aligned so that atomic ops
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 9717ca8..9f448c6 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -14,6 +14,9 @@
#include <linux/bitops.h>
#include <linux/hardirq.h> /* for in_interrupt() */
#include <linux/hugetlb_inline.h>
+#ifdef CONFIG_LOCKDEP_PAGELOCK
+#include <linux/lockdep.h>
+#endif
/*
* Bits in mapping->flags.
@@ -450,26 +453,91 @@ static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
return pgoff;
}
+#ifdef CONFIG_LOCKDEP_PAGELOCK
+#define lock_page_init(p) \
+do { \
+ static struct lock_class_key __key; \
+ lockdep_init_map_crosslock((struct lockdep_map *)&(p)->map, \
+ "(PG_locked)" #p, &__key, 0); \
+} while (0)
+
+static inline void lock_page_acquire(struct page *page, int try)
+{
+ page = compound_head(page);
+ lock_acquire_exclusive((struct lockdep_map *)&page->map, 0,
+ try, NULL, _RET_IP_);
+}
+
+static inline void lock_page_release(struct page *page)
+{
+ page = compound_head(page);
+ /*
+ * lock_commit_crosslock() is necessary for crosslocks.
+ */
+ lock_commit_crosslock((struct lockdep_map *)&page->map);
+ lock_release((struct lockdep_map *)&page->map, 0, _RET_IP_);
+}
+#else
+static inline void lock_page_init(struct page *page) {}
+static inline void lock_page_free(struct page *page) {}
+static inline void lock_page_acquire(struct page *page, int try) {}
+static inline void lock_page_release(struct page *page) {}
+#endif
+
extern void __lock_page(struct page *page);
extern int __lock_page_killable(struct page *page);
extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags);
-extern void unlock_page(struct page *page);
+extern void do_raw_unlock_page(struct page *page);
-static inline int trylock_page(struct page *page)
+static inline void unlock_page(struct page *page)
+{
+ lock_page_release(page);
+ do_raw_unlock_page(page);
+}
+
+static inline int do_raw_trylock_page(struct page *page)
{
page = compound_head(page);
return (likely(!test_and_set_bit_lock(PG_locked, &page->flags)));
}
+static inline int trylock_page(struct page *page)
+{
+ if (do_raw_trylock_page(page)) {
+ lock_page_acquire(page, 1);
+ return 1;
+ }
+ return 0;
+}
+
/*
* lock_page may only be called if we have the page's inode pinned.
*/
static inline void lock_page(struct page *page)
{
might_sleep();
- if (!trylock_page(page))
+
+ if (!do_raw_trylock_page(page))
__lock_page(page);
+ /*
+ * acquire() must be after actual lock operation for crosslocks.
+ * This way a crosslock and current lock can be ordered like:
+ *
+ * CONTEXT 1 CONTEXT 2
+ * --------- ---------
+ * lock A (cross)
+ * acquire A
+ * X = atomic_inc_return(&cross_gen_id)
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ * acquire B
+ * Y = atomic_read_acquire(&cross_gen_id)
+ * lock B
+ *
+ * so that 'lock A and then lock B' can be seen globally,
+ * if X <= Y.
+ */
+ lock_page_acquire(page, 0);
}
/*
@@ -479,9 +547,20 @@ static inline void lock_page(struct page *page)
*/
static inline int lock_page_killable(struct page *page)
{
+ int ret;
+
might_sleep();
- if (!trylock_page(page))
- return __lock_page_killable(page);
+
+ if (!do_raw_trylock_page(page)) {
+ ret = __lock_page_killable(page);
+ if (ret)
+ return ret;
+ }
+ /*
+ * acquire() must be after actual lock operation for crosslocks.
+ * This way a crosslock and other locks can be ordered.
+ */
+ lock_page_acquire(page, 0);
return 0;
}
@@ -496,7 +575,17 @@ static inline int lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags)
{
might_sleep();
- return trylock_page(page) || __lock_page_or_retry(page, mm, flags);
+
+ if (do_raw_trylock_page(page) || __lock_page_or_retry(page, mm, flags)) {
+ /*
+ * acquire() must be after actual lock operation for crosslocks.
+ * This way a crosslock and other locks can be ordered.
+ */
+ lock_page_acquire(page, 0);
+ return 1;
+ }
+
+ return 0;
}
/*
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 4ba8adc..99b5f76 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1093,6 +1093,14 @@ config LOCKDEP_COMPLETE
A deadlock caused by wait_for_completion() and complete() can be
detected by lockdep using crossrelease feature.
+config LOCKDEP_PAGELOCK
+ bool "Lock debugging: allow PG_locked lock to use deadlock detector"
+ select LOCKDEP_CROSSRELEASE
+ default n
+ help
+ PG_locked lock is a kind of crosslock. Using crossrelease feature,
+ PG_locked lock can work with runtime deadlock detector.
+
config PROVE_LOCKING
bool "Lock debugging: prove locking correctness"
depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
diff --git a/mm/filemap.c b/mm/filemap.c
index a497024..0d83bf0 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1083,7 +1083,7 @@ static inline bool clear_bit_unlock_is_negative_byte(long nr, volatile void *mem
* portably (architectures that do LL/SC can test any bit, while x86 can
* test the sign bit).
*/
-void unlock_page(struct page *page)
+void do_raw_unlock_page(struct page *page)
{
BUILD_BUG_ON(PG_waiters != 7);
page = compound_head(page);
@@ -1091,7 +1091,7 @@ void unlock_page(struct page *page)
if (clear_bit_unlock_is_negative_byte(PG_locked, &page->flags))
wake_up_page_bit(page, PG_locked);
}
-EXPORT_SYMBOL(unlock_page);
+EXPORT_SYMBOL(do_raw_unlock_page);
/**
* end_page_writeback - end writeback against a page
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6d30e91..2cbf412 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5406,6 +5406,9 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
} else {
__init_single_pfn(pfn, zone, nid);
}
+#ifdef CONFIG_LOCKDEP_PAGELOCK
+ lock_page_init(pfn_to_page(pfn));
+#endif
}
}
--
1.9.1
[toc] | [prev] | [next] | [standalone]
| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-10 03:40 +0200 |
| Subject | Re: [PATCH v8 11/14] lockdep: Apply crossrelease to PG_locked locks |
| Message-ID | <ucKC6-79t-3@gated-at.bofh.it> |
| In reply to | #1705155 |
On Mon, Aug 07, 2017 at 04:12:58PM +0900, Byungchul Park wrote: > Although lock_page() and its family can cause deadlock, the lock > correctness validator could not be applied to them until now, becasue > things like unlock_page() might be called in a different context from > the acquisition context, which violates lockdep's assumption. > > Thanks to CONFIG_LOCKDEP_CROSSRELEASE, we can now apply the lockdep > detector to page locks. Applied it. Is there any reason excluding applying it into PG_locked?
[toc] | [prev] | [next] | [standalone]
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Date | 2017-08-10 11:30 +0200 |
| Subject | Re: [PATCH v8 11/14] lockdep: Apply crossrelease to PG_locked locks |
| Message-ID | <ucRWX-3Ia-31@gated-at.bofh.it> |
| In reply to | #1708128 |
On Thu, Aug 10, 2017 at 10:35:02AM +0900, Byungchul Park wrote: > On Mon, Aug 07, 2017 at 04:12:58PM +0900, Byungchul Park wrote: > > Although lock_page() and its family can cause deadlock, the lock > > correctness validator could not be applied to them until now, becasue > > things like unlock_page() might be called in a different context from > > the acquisition context, which violates lockdep's assumption. > > > > Thanks to CONFIG_LOCKDEP_CROSSRELEASE, we can now apply the lockdep > > detector to page locks. Applied it. > > Is there any reason excluding applying it into PG_locked? Wanted to start small..
[toc] | [prev] | [next] | [standalone]
| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-07 09:20 +0200 |
| Subject | [PATCH v8 10/14] pagemap.h: Remove trailing white space |
| Message-ID | <ubKuu-59V-29@gated-at.bofh.it> |
| In reply to | #1705149 |
Trailing white space is not accepted in kernel coding style. Remove them. Signed-off-by: Byungchul Park <byungchul.park@lge.com> --- include/linux/pagemap.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index baa9344..9717ca8 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -506,7 +506,7 @@ static inline int lock_page_or_retry(struct page *page, struct mm_struct *mm, extern void wait_on_page_bit(struct page *page, int bit_nr); extern int wait_on_page_bit_killable(struct page *page, int bit_nr); -/* +/* * Wait for a page to be unlocked. * * This must be called with the caller "holding" the page, @@ -526,7 +526,7 @@ static inline int wait_on_page_locked_killable(struct page *page) return wait_on_page_bit_killable(compound_head(page), PG_locked); } -/* +/* * Wait for a page to complete writeback */ static inline void wait_on_page_writeback(struct page *page) -- 1.9.1
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| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-07 09:20 +0200 |
| Subject | [PATCH v8 07/14] lockdep: Handle non(or multi)-acquisition of a crosslock |
| Message-ID | <ubKuu-59V-31@gated-at.bofh.it> |
| In reply to | #1705149 |
No acquisition might be in progress on commit of a crosslock. Completion
operations enabling crossrelease are the case like:
CONTEXT X CONTEXT Y
--------- ---------
trigger completion context
complete AX
commit AX
wait_for_complete AX
acquire AX
wait
where AX is a crosslock.
When no acquisition is in progress, we should not perform commit because
the lock does not exist, which might cause incorrect memory access. So
we have to track the number of acquisitions of a crosslock to handle it.
Moreover, in case that more than one acquisition of a crosslock are
overlapped like:
CONTEXT W CONTEXT X CONTEXT Y CONTEXT Z
--------- --------- --------- ---------
acquire AX (gen_id: 1)
acquire A
acquire AX (gen_id: 10)
acquire B
commit AX
acquire C
commit AX
where A, B and C are typical locks and AX is a crosslock.
Current crossrelease code performs commits in Y and Z with gen_id = 10.
However, we can use gen_id = 1 to do it, since not only 'acquire AX in X'
but 'acquire AX in W' also depends on each acquisition in Y and Z until
their commits. So make it use gen_id = 1 instead of 10 on their commits,
which adds an additional dependency 'AX -> A' in the example above.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
include/linux/lockdep.h | 22 ++++++++++++-
kernel/locking/lockdep.c | 82 +++++++++++++++++++++++++++++++++---------------
2 files changed, 77 insertions(+), 27 deletions(-)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 48c244c..54916f7 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -325,6 +325,19 @@ struct hist_lock {
*/
struct cross_lock {
/*
+ * When more than one acquisition of crosslocks are overlapped,
+ * we have to perform commit for them based on cross_gen_id of
+ * the first acquisition, which allows us to add more true
+ * dependencies.
+ *
+ * Moreover, when no acquisition of a crosslock is in progress,
+ * we should not perform commit because the lock might not exist
+ * any more, which might cause incorrect memory access. So we
+ * have to track the number of acquisitions of a crosslock.
+ */
+ int nr_acquire;
+
+ /*
* Seperate hlock instance. This will be used at commit step.
*
* TODO: Use a smaller data structure containing only necessary
@@ -554,9 +567,16 @@ extern void lockdep_init_map_crosslock(struct lockdep_map *lock,
int subclass);
extern void lock_commit_crosslock(struct lockdep_map *lock);
+/*
+ * What we essencially have to initialize is 'nr_acquire'. Other members
+ * will be initialized in add_xlock().
+ */
+#define STATIC_CROSS_LOCK_INIT() \
+ { .nr_acquire = 0,}
+
#define STATIC_CROSS_LOCKDEP_MAP_INIT(_name, _key) \
{ .map.name = (_name), .map.key = (void *)(_key), \
- .map.cross = 1, }
+ .map.cross = 1, .xlock = STATIC_CROSS_LOCK_INIT(), }
/*
* To initialize a lockdep_map statically use this macro.
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 5168dac..4eae7dc 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4928,11 +4928,28 @@ static int add_xlock(struct held_lock *hlock)
xlock = &((struct lockdep_map_cross *)hlock->instance)->xlock;
+ /*
+ * When acquisitions for a crosslock are overlapped, we use
+ * nr_acquire to perform commit for them, based on cross_gen_id
+ * of the first acquisition, which allows to add additional
+ * dependencies.
+ *
+ * Moreover, when no acquisition of a crosslock is in progress,
+ * we should not perform commit because the lock might not exist
+ * any more, which might cause incorrect memory access. So we
+ * have to track the number of acquisitions of a crosslock.
+ *
+ * depend_after() is necessary to initialize only the first
+ * valid xlock so that the xlock can be used on its commit.
+ */
+ if (xlock->nr_acquire++ && depend_after(&xlock->hlock))
+ goto unlock;
+
gen_id = (unsigned int)atomic_inc_return(&cross_gen_id);
xlock->hlock = *hlock;
xlock->hlock.gen_id = gen_id;
+unlock:
graph_unlock();
-
return 1;
}
@@ -5028,35 +5045,37 @@ static void commit_xhlocks(struct cross_lock *xlock)
if (!graph_lock())
return;
- for (i = 0; i < MAX_XHLOCKS_NR; i++) {
- struct hist_lock *xhlock = &xhlock(cur - i);
+ if (xlock->nr_acquire) {
+ for (i = 0; i < MAX_XHLOCKS_NR; i++) {
+ struct hist_lock *xhlock = &xhlock(cur - i);
- if (!xhlock_valid(xhlock))
- break;
+ if (!xhlock_valid(xhlock))
+ break;
- if (before(xhlock->hlock.gen_id, xlock->hlock.gen_id))
- break;
+ if (before(xhlock->hlock.gen_id, xlock->hlock.gen_id))
+ break;
- if (!same_context_xhlock(xhlock))
- break;
+ if (!same_context_xhlock(xhlock))
+ break;
- /*
- * Filter out the cases that the ring buffer was
- * overwritten and the previous entry has a bigger
- * hist_id than the following one, which is impossible
- * otherwise.
- */
- if (unlikely(before(xhlock->hist_id, prev_hist_id)))
- break;
+ /*
+ * Filter out the cases that the ring buffer was
+ * overwritten and the previous entry has a bigger
+ * hist_id than the following one, which is impossible
+ * otherwise.
+ */
+ if (unlikely(before(xhlock->hist_id, prev_hist_id)))
+ break;
- prev_hist_id = xhlock->hist_id;
+ prev_hist_id = xhlock->hist_id;
- /*
- * commit_xhlock() returns 0 with graph_lock already
- * released if fail.
- */
- if (!commit_xhlock(xlock, xhlock))
- return;
+ /*
+ * commit_xhlock() returns 0 with graph_lock already
+ * released if fail.
+ */
+ if (!commit_xhlock(xlock, xhlock))
+ return;
+ }
}
graph_unlock();
@@ -5100,16 +5119,27 @@ void lock_commit_crosslock(struct lockdep_map *lock)
EXPORT_SYMBOL_GPL(lock_commit_crosslock);
/*
- * Return: 1 - crosslock, done;
+ * Return: 0 - failure;
+ * 1 - crosslock, done;
* 2 - normal lock, continue to held_lock[] ops.
*/
static int lock_release_crosslock(struct lockdep_map *lock)
{
- return cross_lock(lock) ? 1 : 2;
+ if (cross_lock(lock)) {
+ if (!graph_lock())
+ return 0;
+ ((struct lockdep_map_cross *)lock)->xlock.nr_acquire--;
+ graph_unlock();
+ return 1;
+ }
+ return 2;
}
static void cross_init(struct lockdep_map *lock, int cross)
{
+ if (cross)
+ ((struct lockdep_map_cross *)lock)->xlock.nr_acquire = 0;
+
lock->cross = cross;
/*
--
1.9.1
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| From | tip-bot for Byungchul Park <tipbot@zytor.com> |
|---|---|
| Date | 2017-08-10 14:30 +0200 |
| Subject | [tip:locking/core] locking/lockdep: Handle non(or multi)-acquisition of a crosslock |
| Message-ID | <ucUL7-5wC-3@gated-at.bofh.it> |
| In reply to | #1705157 |
Commit-ID: 28a903f63ec0811ead70ad0f8665e838d207a25e
Gitweb: http://git.kernel.org/tip/28a903f63ec0811ead70ad0f8665e838d207a25e
Author: Byungchul Park <byungchul.park@lge.com>
AuthorDate: Mon, 7 Aug 2017 16:12:54 +0900
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 10 Aug 2017 12:29:08 +0200
locking/lockdep: Handle non(or multi)-acquisition of a crosslock
No acquisition might be in progress on commit of a crosslock. Completion
operations enabling crossrelease are the case like:
CONTEXT X CONTEXT Y
--------- ---------
trigger completion context
complete AX
commit AX
wait_for_complete AX
acquire AX
wait
where AX is a crosslock.
When no acquisition is in progress, we should not perform commit because
the lock does not exist, which might cause incorrect memory access. So
we have to track the number of acquisitions of a crosslock to handle it.
Moreover, in case that more than one acquisition of a crosslock are
overlapped like:
CONTEXT W CONTEXT X CONTEXT Y CONTEXT Z
--------- --------- --------- ---------
acquire AX (gen_id: 1)
acquire A
acquire AX (gen_id: 10)
acquire B
commit AX
acquire C
commit AX
where A, B and C are typical locks and AX is a crosslock.
Current crossrelease code performs commits in Y and Z with gen_id = 10.
However, we can use gen_id = 1 to do it, since not only 'acquire AX in X'
but 'acquire AX in W' also depends on each acquisition in Y and Z until
their commits. So make it use gen_id = 1 instead of 10 on their commits,
which adds an additional dependency 'AX -> A' in the example above.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akpm@linux-foundation.org
Cc: boqun.feng@gmail.com
Cc: kernel-team@lge.com
Cc: kirill@shutemov.name
Cc: npiggin@gmail.com
Cc: walken@google.com
Cc: willy@infradead.org
Link: http://lkml.kernel.org/r/1502089981-21272-8-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/linux/lockdep.h | 22 ++++++++++++-
kernel/locking/lockdep.c | 82 +++++++++++++++++++++++++++++++++---------------
2 files changed, 77 insertions(+), 27 deletions(-)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index c75eedd..651cc61 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -325,6 +325,19 @@ struct hist_lock {
*/
struct cross_lock {
/*
+ * When more than one acquisition of crosslocks are overlapped,
+ * we have to perform commit for them based on cross_gen_id of
+ * the first acquisition, which allows us to add more true
+ * dependencies.
+ *
+ * Moreover, when no acquisition of a crosslock is in progress,
+ * we should not perform commit because the lock might not exist
+ * any more, which might cause incorrect memory access. So we
+ * have to track the number of acquisitions of a crosslock.
+ */
+ int nr_acquire;
+
+ /*
* Seperate hlock instance. This will be used at commit step.
*
* TODO: Use a smaller data structure containing only necessary
@@ -547,9 +560,16 @@ extern void lockdep_init_map_crosslock(struct lockdep_map *lock,
int subclass);
extern void lock_commit_crosslock(struct lockdep_map *lock);
+/*
+ * What we essencially have to initialize is 'nr_acquire'. Other members
+ * will be initialized in add_xlock().
+ */
+#define STATIC_CROSS_LOCK_INIT() \
+ { .nr_acquire = 0,}
+
#define STATIC_CROSS_LOCKDEP_MAP_INIT(_name, _key) \
{ .map.name = (_name), .map.key = (void *)(_key), \
- .map.cross = 1, }
+ .map.cross = 1, .xlock = STATIC_CROSS_LOCK_INIT(), }
/*
* To initialize a lockdep_map statically use this macro.
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index eda8114..7f97871 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4867,11 +4867,28 @@ static int add_xlock(struct held_lock *hlock)
xlock = &((struct lockdep_map_cross *)hlock->instance)->xlock;
+ /*
+ * When acquisitions for a crosslock are overlapped, we use
+ * nr_acquire to perform commit for them, based on cross_gen_id
+ * of the first acquisition, which allows to add additional
+ * dependencies.
+ *
+ * Moreover, when no acquisition of a crosslock is in progress,
+ * we should not perform commit because the lock might not exist
+ * any more, which might cause incorrect memory access. So we
+ * have to track the number of acquisitions of a crosslock.
+ *
+ * depend_after() is necessary to initialize only the first
+ * valid xlock so that the xlock can be used on its commit.
+ */
+ if (xlock->nr_acquire++ && depend_after(&xlock->hlock))
+ goto unlock;
+
gen_id = (unsigned int)atomic_inc_return(&cross_gen_id);
xlock->hlock = *hlock;
xlock->hlock.gen_id = gen_id;
+unlock:
graph_unlock();
-
return 1;
}
@@ -4967,35 +4984,37 @@ static void commit_xhlocks(struct cross_lock *xlock)
if (!graph_lock())
return;
- for (i = 0; i < MAX_XHLOCKS_NR; i++) {
- struct hist_lock *xhlock = &xhlock(cur - i);
+ if (xlock->nr_acquire) {
+ for (i = 0; i < MAX_XHLOCKS_NR; i++) {
+ struct hist_lock *xhlock = &xhlock(cur - i);
- if (!xhlock_valid(xhlock))
- break;
+ if (!xhlock_valid(xhlock))
+ break;
- if (before(xhlock->hlock.gen_id, xlock->hlock.gen_id))
- break;
+ if (before(xhlock->hlock.gen_id, xlock->hlock.gen_id))
+ break;
- if (!same_context_xhlock(xhlock))
- break;
+ if (!same_context_xhlock(xhlock))
+ break;
- /*
- * Filter out the cases that the ring buffer was
- * overwritten and the previous entry has a bigger
- * hist_id than the following one, which is impossible
- * otherwise.
- */
- if (unlikely(before(xhlock->hist_id, prev_hist_id)))
- break;
+ /*
+ * Filter out the cases that the ring buffer was
+ * overwritten and the previous entry has a bigger
+ * hist_id than the following one, which is impossible
+ * otherwise.
+ */
+ if (unlikely(before(xhlock->hist_id, prev_hist_id)))
+ break;
- prev_hist_id = xhlock->hist_id;
+ prev_hist_id = xhlock->hist_id;
- /*
- * commit_xhlock() returns 0 with graph_lock already
- * released if fail.
- */
- if (!commit_xhlock(xlock, xhlock))
- return;
+ /*
+ * commit_xhlock() returns 0 with graph_lock already
+ * released if fail.
+ */
+ if (!commit_xhlock(xlock, xhlock))
+ return;
+ }
}
graph_unlock();
@@ -5039,16 +5058,27 @@ void lock_commit_crosslock(struct lockdep_map *lock)
EXPORT_SYMBOL_GPL(lock_commit_crosslock);
/*
- * Return: 1 - crosslock, done;
+ * Return: 0 - failure;
+ * 1 - crosslock, done;
* 2 - normal lock, continue to held_lock[] ops.
*/
static int lock_release_crosslock(struct lockdep_map *lock)
{
- return cross_lock(lock) ? 1 : 2;
+ if (cross_lock(lock)) {
+ if (!graph_lock())
+ return 0;
+ ((struct lockdep_map_cross *)lock)->xlock.nr_acquire--;
+ graph_unlock();
+ return 1;
+ }
+ return 2;
}
static void cross_init(struct lockdep_map *lock, int cross)
{
+ if (cross)
+ ((struct lockdep_map_cross *)lock)->xlock.nr_acquire = 0;
+
lock->cross = cross;
/*
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| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-07 09:20 +0200 |
| Subject | [PATCH v8 12/14] lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked |
| Message-ID | <ubKuu-59V-33@gated-at.bofh.it> |
| In reply to | #1705149 |
Usually PG_locked bit is updated by lock_page() or unlock_page().
However, it can be also updated through __SetPageLocked() or
__ClearPageLockded(). They have to be considered, to get paired between
acquire and release.
Furthermore, e.g. __SetPageLocked() in add_to_page_cache_lru() is called
frequently. We might miss many chances to check deadlock if we ignore it.
Make __Set(__Clear)PageLockded considered as well.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
include/linux/page-flags.h | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index d33e328..b793342 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -261,7 +261,6 @@ static __always_inline int PageCompound(struct page *page)
#define TESTSCFLAG_FALSE(uname) \
TESTSETFLAG_FALSE(uname) TESTCLEARFLAG_FALSE(uname)
-__PAGEFLAG(Locked, locked, PF_NO_TAIL)
PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) __CLEARPAGEFLAG(Waiters, waiters, PF_ONLY_HEAD)
PAGEFLAG(Error, error, PF_NO_COMPOUND) TESTCLEARFLAG(Error, error, PF_NO_COMPOUND)
PAGEFLAG(Referenced, referenced, PF_HEAD)
@@ -373,6 +372,35 @@ static __always_inline int PageSwapCache(struct page *page)
PAGEFLAG(Idle, idle, PF_ANY)
#endif
+#ifdef CONFIG_LOCKDEP_PAGELOCK
+#include <linux/lockdep.h>
+
+TESTPAGEFLAG(Locked, locked, PF_NO_TAIL)
+
+static __always_inline void __SetPageLocked(struct page *page)
+{
+ __set_bit(PG_locked, &PF_NO_TAIL(page, 1)->flags);
+
+ page = compound_head(page);
+ lock_acquire_exclusive((struct lockdep_map *)&page->map, 0, 1, NULL, _RET_IP_);
+}
+
+static __always_inline void __ClearPageLocked(struct page *page)
+{
+ __clear_bit(PG_locked, &PF_NO_TAIL(page, 1)->flags);
+
+ page = compound_head(page);
+ /*
+ * lock_commit_crosslock() is necessary for crosslock
+ * when the lock is released, before lock_release().
+ */
+ lock_commit_crosslock((struct lockdep_map *)&page->map);
+ lock_release((struct lockdep_map *)&page->map, 0, _RET_IP_);
+}
+#else
+__PAGEFLAG(Locked, locked, PF_NO_TAIL)
+#endif
+
/*
* On an anonymous page mapped into a user virtual memory area,
* page->mapping points to its anon_vma, not to a struct address_space;
--
1.9.1
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| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-07 09:20 +0200 |
| Subject | [PATCH v8 14/14] lockdep: Crossrelease feature documentation |
| Message-ID | <ubKuv-59V-35@gated-at.bofh.it> |
| In reply to | #1705149 |
This document describes the concept of crossrelease feature. Signed-off-by: Byungchul Park <byungchul.park@lge.com> --- Documentation/locking/crossrelease.txt | 874 +++++++++++++++++++++++++++++++++ 1 file changed, 874 insertions(+) create mode 100644 Documentation/locking/crossrelease.txt diff --git a/Documentation/locking/crossrelease.txt b/Documentation/locking/crossrelease.txt new file mode 100644 index 0000000..bdf1423 --- /dev/null +++ b/Documentation/locking/crossrelease.txt @@ -0,0 +1,874 @@ +Crossrelease +============ + +Started by Byungchul Park <byungchul.park@lge.com> + +Contents: + + (*) Background + + - What causes deadlock + - How lockdep works + + (*) Limitation + + - Limit lockdep + - Pros from the limitation + - Cons from the limitation + - Relax the limitation + + (*) Crossrelease + + - Introduce crossrelease + - Introduce commit + + (*) Implementation + + - Data structures + - How crossrelease works + + (*) Optimizations + + - Avoid duplication + - Lockless for hot paths + + (*) APPENDIX A: What lockdep does to work aggresively + + (*) APPENDIX B: How to avoid adding false dependencies + + +========== +Background +========== + +What causes deadlock +-------------------- + +A deadlock occurs when a context is waiting for an event to happen, +which is impossible because another (or the) context who can trigger the +event is also waiting for another (or the) event to happen, which is +also impossible due to the same reason. + +For example: + + A context going to trigger event C is waiting for event A to happen. + A context going to trigger event A is waiting for event B to happen. + A context going to trigger event B is waiting for event C to happen. + +A deadlock occurs when these three wait operations run at the same time, +because event C cannot be triggered if event A does not happen, which in +turn cannot be triggered if event B does not happen, which in turn +cannot be triggered if event C does not happen. After all, no event can +be triggered since any of them never meets its condition to wake up. + +A dependency might exist between two waiters and a deadlock might happen +due to an incorrect releationship between dependencies. Thus, we must +define what a dependency is first. A dependency exists between them if: + + 1. There are two waiters waiting for each event at a given time. + 2. The only way to wake up each waiter is to trigger its event. + 3. Whether one can be woken up depends on whether the other can. + +Each wait in the example creates its dependency like: + + Event C depends on event A. + Event A depends on event B. + Event B depends on event C. + + NOTE: Precisely speaking, a dependency is one between whether a + waiter for an event can be woken up and whether another waiter for + another event can be woken up. However from now on, we will describe + a dependency as if it's one between an event and another event for + simplicity. + +And they form circular dependencies like: + + -> C -> A -> B - + / \ + \ / + ---------------- + + where 'A -> B' means that event A depends on event B. + +Such circular dependencies lead to a deadlock since no waiter can meet +its condition to wake up as described. + +CONCLUSION + +Circular dependencies cause a deadlock. + + +How lockdep works +----------------- + +Lockdep tries to detect a deadlock by checking dependencies created by +lock operations, acquire and release. Waiting for a lock corresponds to +waiting for an event, and releasing a lock corresponds to triggering an +event in the previous section. + +In short, lockdep does: + + 1. Detect a new dependency. + 2. Add the dependency into a global graph. + 3. Check if that makes dependencies circular. + 4. Report a deadlock or its possibility if so. + +For example, consider a graph built by lockdep that looks like: + + A -> B - + \ + -> E + / + C -> D - + + where A, B,..., E are different lock classes. + +Lockdep will add a dependency into the graph on detection of a new +dependency. For example, it will add a dependency 'E -> C' when a new +dependency between lock E and lock C is detected. Then the graph will be: + + A -> B - + \ + -> E - + / \ + -> C -> D - \ + / / + \ / + ------------------ + + where A, B,..., E are different lock classes. + +This graph contains a subgraph which demonstrates circular dependencies: + + -> E - + / \ + -> C -> D - \ + / / + \ / + ------------------ + + where C, D and E are different lock classes. + +This is the condition under which a deadlock might occur. Lockdep +reports it on detection after adding a new dependency. This is the way +how lockdep works. + +CONCLUSION + +Lockdep detects a deadlock or its possibility by checking if circular +dependencies were created after adding each new dependency. + + +========== +Limitation +========== + +Limit lockdep +------------- + +Limiting lockdep to work on only typical locks e.g. spin locks and +mutexes, which are released within the acquire context, the +implementation becomes simple but its capacity for detection becomes +limited. Let's check pros and cons in next section. + + +Pros from the limitation +------------------------ + +Given the limitation, when acquiring a lock, locks in a held_locks +cannot be released if the context cannot acquire it so has to wait to +acquire it, which means all waiters for the locks in the held_locks are +stuck. It's an exact case to create dependencies between each lock in +the held_locks and the lock to acquire. + +For example: + + CONTEXT X + --------- + acquire A + acquire B /* Add a dependency 'A -> B' */ + release B + release A + + where A and B are different lock classes. + +When acquiring lock A, the held_locks of CONTEXT X is empty thus no +dependency is added. But when acquiring lock B, lockdep detects and adds +a new dependency 'A -> B' between lock A in the held_locks and lock B. +They can be simply added whenever acquiring each lock. + +And data required by lockdep exists in a local structure, held_locks +embedded in task_struct. Forcing to access the data within the context, +lockdep can avoid racy problems without explicit locks while handling +the local data. + +Lastly, lockdep only needs to keep locks currently being held, to build +a dependency graph. However, relaxing the limitation, it needs to keep +even locks already released, because a decision whether they created +dependencies might be long-deferred. + +To sum up, we can expect several advantages from the limitation: + + 1. Lockdep can easily identify a dependency when acquiring a lock. + 2. Races are avoidable while accessing local locks in a held_locks. + 3. Lockdep only needs to keep locks currently being held. + +CONCLUSION + +Given the limitation, the implementation becomes simple and efficient. + + +Cons from the limitation +------------------------ + +Given the limitation, lockdep is applicable only to typical locks. For +example, page locks for page access or completions for synchronization +cannot work with lockdep. + +Can we detect deadlocks below, under the limitation? + +Example 1: + + CONTEXT X CONTEXT Y CONTEXT Z + --------- --------- ---------- + mutex_lock A + lock_page B + lock_page B + mutex_lock A /* DEADLOCK */ + unlock_page B held by X + unlock_page B + mutex_unlock A + mutex_unlock A + + where A and B are different lock classes. + +No, we cannot. + +Example 2: + + CONTEXT X CONTEXT Y + --------- --------- + mutex_lock A + mutex_lock A + wait_for_complete B /* DEADLOCK */ + complete B + mutex_unlock A + mutex_unlock A + + where A is a lock class and B is a completion variable. + +No, we cannot. + +CONCLUSION + +Given the limitation, lockdep cannot detect a deadlock or its +possibility caused by page locks or completions. + + +Relax the limitation +-------------------- + +Under the limitation, things to create dependencies are limited to +typical locks. However, synchronization primitives like page locks and +completions, which are allowed to be released in any context, also +create dependencies and can cause a deadlock. So lockdep should track +these locks to do a better job. We have to relax the limitation for +these locks to work with lockdep. + +Detecting dependencies is very important for lockdep to work because +adding a dependency means adding an opportunity to check whether it +causes a deadlock. The more lockdep adds dependencies, the more it +thoroughly works. Thus Lockdep has to do its best to detect and add as +many true dependencies into a graph as possible. + +For example, considering only typical locks, lockdep builds a graph like: + + A -> B - + \ + -> E + / + C -> D - + + where A, B,..., E are different lock classes. + +On the other hand, under the relaxation, additional dependencies might +be created and added. Assuming additional 'FX -> C' and 'E -> GX' are +added thanks to the relaxation, the graph will be: + + A -> B - + \ + -> E -> GX + / + FX -> C -> D - + + where A, B,..., E, FX and GX are different lock classes, and a suffix + 'X' is added on non-typical locks. + +The latter graph gives us more chances to check circular dependencies +than the former. However, it might suffer performance degradation since +relaxing the limitation, with which design and implementation of lockdep +can be efficient, might introduce inefficiency inevitably. So lockdep +should provide two options, strong detection and efficient detection. + +Choosing efficient detection: + + Lockdep works with only locks restricted to be released within the + acquire context. However, lockdep works efficiently. + +Choosing strong detection: + + Lockdep works with all synchronization primitives. However, lockdep + suffers performance degradation. + +CONCLUSION + +Relaxing the limitation, lockdep can add additional dependencies giving +additional opportunities to check circular dependencies. + + +============ +Crossrelease +============ + +Introduce crossrelease +---------------------- + +In order to allow lockdep to handle additional dependencies by what +might be released in any context, namely 'crosslock', we have to be able +to identify those created by crosslocks. The proposed 'crossrelease' +feature provoides a way to do that. + +Crossrelease feature has to do: + + 1. Identify dependencies created by crosslocks. + 2. Add the dependencies into a dependency graph. + +That's all. Once a meaningful dependency is added into graph, then +lockdep would work with the graph as it did. The most important thing +crossrelease feature has to do is to correctly identify and add true +dependencies into the global graph. + +A dependency e.g. 'A -> B' can be identified only in the A's release +context because a decision required to identify the dependency can be +made only in the release context. That is to decide whether A can be +released so that a waiter for A can be woken up. It cannot be made in +other than the A's release context. + +It's no matter for typical locks because each acquire context is same as +its release context, thus lockdep can decide whether a lock can be +released in the acquire context. However for crosslocks, lockdep cannot +make the decision in the acquire context but has to wait until the +release context is identified. + +Therefore, deadlocks by crosslocks cannot be detected just when it +happens, because those cannot be identified until the crosslocks are +released. However, deadlock possibilities can be detected and it's very +worth. See 'APPENDIX A' section to check why. + +CONCLUSION + +Using crossrelease feature, lockdep can work with what might be released +in any context, namely crosslock. + + +Introduce commit +---------------- + +Since crossrelease defers the work adding true dependencies of +crosslocks until they are actually released, crossrelease has to queue +all acquisitions which might create dependencies with the crosslocks. +Then it identifies dependencies using the queued data in batches at a +proper time. We call it 'commit'. + +There are four types of dependencies: + +1. TT type: 'typical lock A -> typical lock B' + + Just when acquiring B, lockdep can see it's in the A's release + context. So the dependency between A and B can be identified + immediately. Commit is unnecessary. + +2. TC type: 'typical lock A -> crosslock BX' + + Just when acquiring BX, lockdep can see it's in the A's release + context. So the dependency between A and BX can be identified + immediately. Commit is unnecessary, too. + +3. CT type: 'crosslock AX -> typical lock B' + + When acquiring B, lockdep cannot identify the dependency because + there's no way to know if it's in the AX's release context. It has + to wait until the decision can be made. Commit is necessary. + +4. CC type: 'crosslock AX -> crosslock BX' + + When acquiring BX, lockdep cannot identify the dependency because + there's no way to know if it's in the AX's release context. It has + to wait until the decision can be made. Commit is necessary. + But, handling CC type is not implemented yet. It's a future work. + +Lockdep can work without commit for typical locks, but commit step is +necessary once crosslocks are involved. Introducing commit, lockdep +performs three steps. What lockdep does in each step is: + +1. Acquisition: For typical locks, lockdep does what it originally did + and queues the lock so that CT type dependencies can be checked using + it at the commit step. For crosslocks, it saves data which will be + used at the commit step and increases a reference count for it. + +2. Commit: No action is reauired for typical locks. For crosslocks, + lockdep adds CT type dependencies using the data saved at the + acquisition step. + +3. Release: No changes are required for typical locks. When a crosslock + is released, it decreases a reference count for it. + +CONCLUSION + +Crossrelease introduces commit step to handle dependencies of crosslocks +in batches at a proper time. + + +============== +Implementation +============== + +Data structures +--------------- + +Crossrelease introduces two main data structures. + +1. hist_lock + + This is an array embedded in task_struct, for keeping lock history so + that dependencies can be added using them at the commit step. Since + it's local data, it can be accessed locklessly in the owner context. + The array is filled at the acquisition step and consumed at the + commit step. And it's managed in circular manner. + +2. cross_lock + + One per lockdep_map exists. This is for keeping data of crosslocks + and used at the commit step. + + +How crossrelease works +---------------------- + +It's the key of how crossrelease works, to defer necessary works to an +appropriate point in time and perform in at once at the commit step. +Let's take a look with examples step by step, starting from how lockdep +works without crossrelease for typical locks. + + acquire A /* Push A onto held_locks */ + acquire B /* Push B onto held_locks and add 'A -> B' */ + acquire C /* Push C onto held_locks and add 'B -> C' */ + release C /* Pop C from held_locks */ + release B /* Pop B from held_locks */ + release A /* Pop A from held_locks */ + + where A, B and C are different lock classes. + + NOTE: This document assumes that readers already understand how + lockdep works without crossrelease thus omits details. But there's + one thing to note. Lockdep pretends to pop a lock from held_locks + when releasing it. But it's subtly different from the original pop + operation because lockdep allows other than the top to be poped. + +In this case, lockdep adds 'the top of held_locks -> the lock to acquire' +dependency every time acquiring a lock. + +After adding 'A -> B', a dependency graph will be: + + A -> B + + where A and B are different lock classes. + +And after adding 'B -> C', the graph will be: + + A -> B -> C + + where A, B and C are different lock classes. + +Let's performs commit step even for typical locks to add dependencies. +Of course, commit step is not necessary for them, however, it would work +well because this is a more general way. + + acquire A + /* + * Queue A into hist_locks + * + * In hist_locks: A + * In graph: Empty + */ + + acquire B + /* + * Queue B into hist_locks + * + * In hist_locks: A, B + * In graph: Empty + */ + + acquire C + /* + * Queue C into hist_locks + * + * In hist_locks: A, B, C + * In graph: Empty + */ + + commit C + /* + * Add 'C -> ?' + * Answer the following to decide '?' + * What has been queued since acquire C: Nothing + * + * In hist_locks: A, B, C + * In graph: Empty + */ + + release C + + commit B + /* + * Add 'B -> ?' + * Answer the following to decide '?' + * What has been queued since acquire B: C + * + * In hist_locks: A, B, C + * In graph: 'B -> C' + */ + + release B + + commit A + /* + * Add 'A -> ?' + * Answer the following to decide '?' + * What has been queued since acquire A: B, C + * + * In hist_locks: A, B, C + * In graph: 'B -> C', 'A -> B', 'A -> C' + */ + + release A + + where A, B and C are different lock classes. + +In this case, dependencies are added at the commit step as described. + +After commits for A, B and C, the graph will be: + + A -> B -> C + + where A, B and C are different lock classes. + + NOTE: A dependency 'A -> C' is optimized out. + +We can see the former graph built without commit step is same as the +latter graph built using commit steps. Of course the former way leads to +earlier finish for building the graph, which means we can detect a +deadlock or its possibility sooner. So the former way would be prefered +when possible. But we cannot avoid using the latter way for crosslocks. + +Let's look at how commit steps work for crosslocks. In this case, the +commit step is performed only on crosslock AX as real. And it assumes +that the AX release context is different from the AX acquire context. + + BX RELEASE CONTEXT BX ACQUIRE CONTEXT + ------------------ ------------------ + acquire A + /* + * Push A onto held_locks + * Queue A into hist_locks + * + * In held_locks: A + * In hist_locks: A + * In graph: Empty + */ + + acquire BX + /* + * Add 'the top of held_locks -> BX' + * + * In held_locks: A + * In hist_locks: A + * In graph: 'A -> BX' + */ + + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + It must be guaranteed that the following operations are seen after + acquiring BX globally. It can be done by things like barrier. + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + + acquire C + /* + * Push C onto held_locks + * Queue C into hist_locks + * + * In held_locks: C + * In hist_locks: C + * In graph: 'A -> BX' + */ + + release C + /* + * Pop C from held_locks + * + * In held_locks: Empty + * In hist_locks: C + * In graph: 'A -> BX' + */ + acquire D + /* + * Push D onto held_locks + * Queue D into hist_locks + * Add 'the top of held_locks -> D' + * + * In held_locks: A, D + * In hist_locks: A, D + * In graph: 'A -> BX', 'A -> D' + */ + acquire E + /* + * Push E onto held_locks + * Queue E into hist_locks + * + * In held_locks: E + * In hist_locks: C, E + * In graph: 'A -> BX', 'A -> D' + */ + + release E + /* + * Pop E from held_locks + * + * In held_locks: Empty + * In hist_locks: D, E + * In graph: 'A -> BX', 'A -> D' + */ + release D + /* + * Pop D from held_locks + * + * In held_locks: A + * In hist_locks: A, D + * In graph: 'A -> BX', 'A -> D' + */ + commit BX + /* + * Add 'BX -> ?' + * What has been queued since acquire BX: C, E + * + * In held_locks: Empty + * In hist_locks: D, E + * In graph: 'A -> BX', 'A -> D', + * 'BX -> C', 'BX -> E' + */ + + release BX + /* + * In held_locks: Empty + * In hist_locks: D, E + * In graph: 'A -> BX', 'A -> D', + * 'BX -> C', 'BX -> E' + */ + release A + /* + * Pop A from held_locks + * + * In held_locks: Empty + * In hist_locks: A, D + * In graph: 'A -> BX', 'A -> D', + * 'BX -> C', 'BX -> E' + */ + + where A, BX, C,..., E are different lock classes, and a suffix 'X' is + added on crosslocks. + +Crossrelease considers all acquisitions after acqiuring BX are +candidates which might create dependencies with BX. True dependencies +will be determined when identifying the release context of BX. Meanwhile, +all typical locks are queued so that they can be used at the commit step. +And then two dependencies 'BX -> C' and 'BX -> E' are added at the +commit step when identifying the release context. + +The final graph will be, with crossrelease: + + -> C + / + -> BX - + / \ + A - -> E + \ + -> D + + where A, BX, C,..., E are different lock classes, and a suffix 'X' is + added on crosslocks. + +However, the final graph will be, without crossrelease: + + A -> D + + where A and D are different lock classes. + +The former graph has three more dependencies, 'A -> BX', 'BX -> C' and +'BX -> E' giving additional opportunities to check if they cause +deadlocks. This way lockdep can detect a deadlock or its possibility +caused by crosslocks. + +CONCLUSION + +We checked how crossrelease works with several examples. + + +============= +Optimizations +============= + +Avoid duplication +----------------- + +Crossrelease feature uses a cache like what lockdep already uses for +dependency chains, but this time it's for caching CT type dependencies. +Once that dependency is cached, the same will never be added again. + + +Lockless for hot paths +---------------------- + +To keep all locks for later use at the commit step, crossrelease adopts +a local array embedded in task_struct, which makes access to the data +lockless by forcing it to happen only within the owner context. It's +like how lockdep handles held_locks. Lockless implmentation is important +since typical locks are very frequently acquired and released. + + +================================================= +APPENDIX A: What lockdep does to work aggresively +================================================= + +A deadlock actually occurs when all wait operations creating circular +dependencies run at the same time. Even though they don't, a potential +deadlock exists if the problematic dependencies exist. Thus it's +meaningful to detect not only an actual deadlock but also its potential +possibility. The latter is rather valuable. When a deadlock occurs +actually, we can identify what happens in the system by some means or +other even without lockdep. However, there's no way to detect possiblity +without lockdep unless the whole code is parsed in head. It's terrible. +Lockdep does the both, and crossrelease only focuses on the latter. + +Whether or not a deadlock actually occurs depends on several factors. +For example, what order contexts are switched in is a factor. Assuming +circular dependencies exist, a deadlock would occur when contexts are +switched so that all wait operations creating the dependencies run +simultaneously. Thus to detect a deadlock possibility even in the case +that it has not occured yet, lockdep should consider all possible +combinations of dependencies, trying to: + +1. Use a global dependency graph. + + Lockdep combines all dependencies into one global graph and uses them, + regardless of which context generates them or what order contexts are + switched in. Aggregated dependencies are only considered so they are + prone to be circular if a problem exists. + +2. Check dependencies between classes instead of instances. + + What actually causes a deadlock are instances of lock. However, + lockdep checks dependencies between classes instead of instances. + This way lockdep can detect a deadlock which has not happened but + might happen in future by others but the same class. + +3. Assume all acquisitions lead to waiting. + + Although locks might be acquired without waiting which is essential + to create dependencies, lockdep assumes all acquisitions lead to + waiting since it might be true some time or another. + +CONCLUSION + +Lockdep detects not only an actual deadlock but also its possibility, +and the latter is more valuable. + + +================================================== +APPENDIX B: How to avoid adding false dependencies +================================================== + +Remind what a dependency is. A dependency exists if: + + 1. There are two waiters waiting for each event at a given time. + 2. The only way to wake up each waiter is to trigger its event. + 3. Whether one can be woken up depends on whether the other can. + +For example: + + acquire A + acquire B /* A dependency 'A -> B' exists */ + release B + release A + + where A and B are different lock classes. + +A depedency 'A -> B' exists since: + + 1. A waiter for A and a waiter for B might exist when acquiring B. + 2. Only way to wake up each is to release what it waits for. + 3. Whether the waiter for A can be woken up depends on whether the + other can. IOW, TASK X cannot release A if it fails to acquire B. + +For another example: + + TASK X TASK Y + ------ ------ + acquire AX + acquire B /* A dependency 'AX -> B' exists */ + release B + release AX held by Y + + where AX and B are different lock classes, and a suffix 'X' is added + on crosslocks. + +Even in this case involving crosslocks, the same rule can be applied. A +depedency 'AX -> B' exists since: + + 1. A waiter for AX and a waiter for B might exist when acquiring B. + 2. Only way to wake up each is to release what it waits for. + 3. Whether the waiter for AX can be woken up depends on whether the + other can. IOW, TASK X cannot release AX if it fails to acquire B. + +Let's take a look at more complicated example: + + TASK X TASK Y + ------ ------ + acquire B + release B + fork Y + acquire AX + acquire C /* A dependency 'AX -> C' exists */ + release C + release AX held by Y + + where AX, B and C are different lock classes, and a suffix 'X' is + added on crosslocks. + +Does a dependency 'AX -> B' exist? Nope. + +Two waiters are essential to create a dependency. However, waiters for +AX and B to create 'AX -> B' cannot exist at the same time in this +example. Thus the dependency 'AX -> B' cannot be created. + +It would be ideal if the full set of true ones can be considered. But +we can ensure nothing but what actually happened. Relying on what +actually happens at runtime, we can anyway add only true ones, though +they might be a subset of true ones. It's similar to how lockdep works +for typical locks. There might be more true dependencies than what +lockdep has detected in runtime. Lockdep has no choice but to rely on +what actually happens. Crossrelease also relies on it. + +CONCLUSION + +Relying on what actually happens, lockdep can avoid adding false +dependencies. -- 1.9.1
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| From | tip-bot for Byungchul Park <tipbot@zytor.com> |
|---|---|
| Date | 2017-08-10 14:30 +0200 |
| Subject | [tip:locking/core] locking/lockdep: Add 'crossrelease' feature documentation |
| Message-ID | <ucUL8-5wC-27@gated-at.bofh.it> |
| In reply to | #1705159 |
Commit-ID: ef0758dd0fd70b98b889af26e27f003656952db8 Gitweb: http://git.kernel.org/tip/ef0758dd0fd70b98b889af26e27f003656952db8 Author: Byungchul Park <byungchul.park@lge.com> AuthorDate: Mon, 7 Aug 2017 16:13:01 +0900 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Thu, 10 Aug 2017 12:32:37 +0200 locking/lockdep: Add 'crossrelease' feature documentation This document describes the concept of crossrelease feature. Signed-off-by: Byungchul Park <byungchul.park@lge.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: akpm@linux-foundation.org Cc: boqun.feng@gmail.com Cc: kernel-team@lge.com Cc: kirill@shutemov.name Cc: npiggin@gmail.com Cc: walken@google.com Cc: willy@infradead.org Link: http://lkml.kernel.org/r/1502089981-21272-15-git-send-email-byungchul.park@lge.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- Documentation/locking/crossrelease.txt | 874 +++++++++++++++++++++++++++++++++ 1 file changed, 874 insertions(+) diff --git a/Documentation/locking/crossrelease.txt b/Documentation/locking/crossrelease.txt new file mode 100644 index 0000000..bdf1423 --- /dev/null +++ b/Documentation/locking/crossrelease.txt @@ -0,0 +1,874 @@ +Crossrelease +============ + +Started by Byungchul Park <byungchul.park@lge.com> + +Contents: + + (*) Background + + - What causes deadlock + - How lockdep works + + (*) Limitation + + - Limit lockdep + - Pros from the limitation + - Cons from the limitation + - Relax the limitation + + (*) Crossrelease + + - Introduce crossrelease + - Introduce commit + + (*) Implementation + + - Data structures + - How crossrelease works + + (*) Optimizations + + - Avoid duplication + - Lockless for hot paths + + (*) APPENDIX A: What lockdep does to work aggresively + + (*) APPENDIX B: How to avoid adding false dependencies + + +========== +Background +========== + +What causes deadlock +-------------------- + +A deadlock occurs when a context is waiting for an event to happen, +which is impossible because another (or the) context who can trigger the +event is also waiting for another (or the) event to happen, which is +also impossible due to the same reason. + +For example: + + A context going to trigger event C is waiting for event A to happen. + A context going to trigger event A is waiting for event B to happen. + A context going to trigger event B is waiting for event C to happen. + +A deadlock occurs when these three wait operations run at the same time, +because event C cannot be triggered if event A does not happen, which in +turn cannot be triggered if event B does not happen, which in turn +cannot be triggered if event C does not happen. After all, no event can +be triggered since any of them never meets its condition to wake up. + +A dependency might exist between two waiters and a deadlock might happen +due to an incorrect releationship between dependencies. Thus, we must +define what a dependency is first. A dependency exists between them if: + + 1. There are two waiters waiting for each event at a given time. + 2. The only way to wake up each waiter is to trigger its event. + 3. Whether one can be woken up depends on whether the other can. + +Each wait in the example creates its dependency like: + + Event C depends on event A. + Event A depends on event B. + Event B depends on event C. + + NOTE: Precisely speaking, a dependency is one between whether a + waiter for an event can be woken up and whether another waiter for + another event can be woken up. However from now on, we will describe + a dependency as if it's one between an event and another event for + simplicity. + +And they form circular dependencies like: + + -> C -> A -> B - + / \ + \ / + ---------------- + + where 'A -> B' means that event A depends on event B. + +Such circular dependencies lead to a deadlock since no waiter can meet +its condition to wake up as described. + +CONCLUSION + +Circular dependencies cause a deadlock. + + +How lockdep works +----------------- + +Lockdep tries to detect a deadlock by checking dependencies created by +lock operations, acquire and release. Waiting for a lock corresponds to +waiting for an event, and releasing a lock corresponds to triggering an +event in the previous section. + +In short, lockdep does: + + 1. Detect a new dependency. + 2. Add the dependency into a global graph. + 3. Check if that makes dependencies circular. + 4. Report a deadlock or its possibility if so. + +For example, consider a graph built by lockdep that looks like: + + A -> B - + \ + -> E + / + C -> D - + + where A, B,..., E are different lock classes. + +Lockdep will add a dependency into the graph on detection of a new +dependency. For example, it will add a dependency 'E -> C' when a new +dependency between lock E and lock C is detected. Then the graph will be: + + A -> B - + \ + -> E - + / \ + -> C -> D - \ + / / + \ / + ------------------ + + where A, B,..., E are different lock classes. + +This graph contains a subgraph which demonstrates circular dependencies: + + -> E - + / \ + -> C -> D - \ + / / + \ / + ------------------ + + where C, D and E are different lock classes. + +This is the condition under which a deadlock might occur. Lockdep +reports it on detection after adding a new dependency. This is the way +how lockdep works. + +CONCLUSION + +Lockdep detects a deadlock or its possibility by checking if circular +dependencies were created after adding each new dependency. + + +========== +Limitation +========== + +Limit lockdep +------------- + +Limiting lockdep to work on only typical locks e.g. spin locks and +mutexes, which are released within the acquire context, the +implementation becomes simple but its capacity for detection becomes +limited. Let's check pros and cons in next section. + + +Pros from the limitation +------------------------ + +Given the limitation, when acquiring a lock, locks in a held_locks +cannot be released if the context cannot acquire it so has to wait to +acquire it, which means all waiters for the locks in the held_locks are +stuck. It's an exact case to create dependencies between each lock in +the held_locks and the lock to acquire. + +For example: + + CONTEXT X + --------- + acquire A + acquire B /* Add a dependency 'A -> B' */ + release B + release A + + where A and B are different lock classes. + +When acquiring lock A, the held_locks of CONTEXT X is empty thus no +dependency is added. But when acquiring lock B, lockdep detects and adds +a new dependency 'A -> B' between lock A in the held_locks and lock B. +They can be simply added whenever acquiring each lock. + +And data required by lockdep exists in a local structure, held_locks +embedded in task_struct. Forcing to access the data within the context, +lockdep can avoid racy problems without explicit locks while handling +the local data. + +Lastly, lockdep only needs to keep locks currently being held, to build +a dependency graph. However, relaxing the limitation, it needs to keep +even locks already released, because a decision whether they created +dependencies might be long-deferred. + +To sum up, we can expect several advantages from the limitation: + + 1. Lockdep can easily identify a dependency when acquiring a lock. + 2. Races are avoidable while accessing local locks in a held_locks. + 3. Lockdep only needs to keep locks currently being held. + +CONCLUSION + +Given the limitation, the implementation becomes simple and efficient. + + +Cons from the limitation +------------------------ + +Given the limitation, lockdep is applicable only to typical locks. For +example, page locks for page access or completions for synchronization +cannot work with lockdep. + +Can we detect deadlocks below, under the limitation? + +Example 1: + + CONTEXT X CONTEXT Y CONTEXT Z + --------- --------- ---------- + mutex_lock A + lock_page B + lock_page B + mutex_lock A /* DEADLOCK */ + unlock_page B held by X + unlock_page B + mutex_unlock A + mutex_unlock A + + where A and B are different lock classes. + +No, we cannot. + +Example 2: + + CONTEXT X CONTEXT Y + --------- --------- + mutex_lock A + mutex_lock A + wait_for_complete B /* DEADLOCK */ + complete B + mutex_unlock A + mutex_unlock A + + where A is a lock class and B is a completion variable. + +No, we cannot. + +CONCLUSION + +Given the limitation, lockdep cannot detect a deadlock or its +possibility caused by page locks or completions. + + +Relax the limitation +-------------------- + +Under the limitation, things to create dependencies are limited to +typical locks. However, synchronization primitives like page locks and +completions, which are allowed to be released in any context, also +create dependencies and can cause a deadlock. So lockdep should track +these locks to do a better job. We have to relax the limitation for +these locks to work with lockdep. + +Detecting dependencies is very important for lockdep to work because +adding a dependency means adding an opportunity to check whether it +causes a deadlock. The more lockdep adds dependencies, the more it +thoroughly works. Thus Lockdep has to do its best to detect and add as +many true dependencies into a graph as possible. + +For example, considering only typical locks, lockdep builds a graph like: + + A -> B - + \ + -> E + / + C -> D - + + where A, B,..., E are different lock classes. + +On the other hand, under the relaxation, additional dependencies might +be created and added. Assuming additional 'FX -> C' and 'E -> GX' are +added thanks to the relaxation, the graph will be: + + A -> B - + \ + -> E -> GX + / + FX -> C -> D - + + where A, B,..., E, FX and GX are different lock classes, and a suffix + 'X' is added on non-typical locks. + +The latter graph gives us more chances to check circular dependencies +than the former. However, it might suffer performance degradation since +relaxing the limitation, with which design and implementation of lockdep +can be efficient, might introduce inefficiency inevitably. So lockdep +should provide two options, strong detection and efficient detection. + +Choosing efficient detection: + + Lockdep works with only locks restricted to be released within the + acquire context. However, lockdep works efficiently. + +Choosing strong detection: + + Lockdep works with all synchronization primitives. However, lockdep + suffers performance degradation. + +CONCLUSION + +Relaxing the limitation, lockdep can add additional dependencies giving +additional opportunities to check circular dependencies. + + +============ +Crossrelease +============ + +Introduce crossrelease +---------------------- + +In order to allow lockdep to handle additional dependencies by what +might be released in any context, namely 'crosslock', we have to be able +to identify those created by crosslocks. The proposed 'crossrelease' +feature provoides a way to do that. + +Crossrelease feature has to do: + + 1. Identify dependencies created by crosslocks. + 2. Add the dependencies into a dependency graph. + +That's all. Once a meaningful dependency is added into graph, then +lockdep would work with the graph as it did. The most important thing +crossrelease feature has to do is to correctly identify and add true +dependencies into the global graph. + +A dependency e.g. 'A -> B' can be identified only in the A's release +context because a decision required to identify the dependency can be +made only in the release context. That is to decide whether A can be +released so that a waiter for A can be woken up. It cannot be made in +other than the A's release context. + +It's no matter for typical locks because each acquire context is same as +its release context, thus lockdep can decide whether a lock can be +released in the acquire context. However for crosslocks, lockdep cannot +make the decision in the acquire context but has to wait until the +release context is identified. + +Therefore, deadlocks by crosslocks cannot be detected just when it +happens, because those cannot be identified until the crosslocks are +released. However, deadlock possibilities can be detected and it's very +worth. See 'APPENDIX A' section to check why. + +CONCLUSION + +Using crossrelease feature, lockdep can work with what might be released +in any context, namely crosslock. + + +Introduce commit +---------------- + +Since crossrelease defers the work adding true dependencies of +crosslocks until they are actually released, crossrelease has to queue +all acquisitions which might create dependencies with the crosslocks. +Then it identifies dependencies using the queued data in batches at a +proper time. We call it 'commit'. + +There are four types of dependencies: + +1. TT type: 'typical lock A -> typical lock B' + + Just when acquiring B, lockdep can see it's in the A's release + context. So the dependency between A and B can be identified + immediately. Commit is unnecessary. + +2. TC type: 'typical lock A -> crosslock BX' + + Just when acquiring BX, lockdep can see it's in the A's release + context. So the dependency between A and BX can be identified + immediately. Commit is unnecessary, too. + +3. CT type: 'crosslock AX -> typical lock B' + + When acquiring B, lockdep cannot identify the dependency because + there's no way to know if it's in the AX's release context. It has + to wait until the decision can be made. Commit is necessary. + +4. CC type: 'crosslock AX -> crosslock BX' + + When acquiring BX, lockdep cannot identify the dependency because + there's no way to know if it's in the AX's release context. It has + to wait until the decision can be made. Commit is necessary. + But, handling CC type is not implemented yet. It's a future work. + +Lockdep can work without commit for typical locks, but commit step is +necessary once crosslocks are involved. Introducing commit, lockdep +performs three steps. What lockdep does in each step is: + +1. Acquisition: For typical locks, lockdep does what it originally did + and queues the lock so that CT type dependencies can be checked using + it at the commit step. For crosslocks, it saves data which will be + used at the commit step and increases a reference count for it. + +2. Commit: No action is reauired for typical locks. For crosslocks, + lockdep adds CT type dependencies using the data saved at the + acquisition step. + +3. Release: No changes are required for typical locks. When a crosslock + is released, it decreases a reference count for it. + +CONCLUSION + +Crossrelease introduces commit step to handle dependencies of crosslocks +in batches at a proper time. + + +============== +Implementation +============== + +Data structures +--------------- + +Crossrelease introduces two main data structures. + +1. hist_lock + + This is an array embedded in task_struct, for keeping lock history so + that dependencies can be added using them at the commit step. Since + it's local data, it can be accessed locklessly in the owner context. + The array is filled at the acquisition step and consumed at the + commit step. And it's managed in circular manner. + +2. cross_lock + + One per lockdep_map exists. This is for keeping data of crosslocks + and used at the commit step. + + +How crossrelease works +---------------------- + +It's the key of how crossrelease works, to defer necessary works to an +appropriate point in time and perform in at once at the commit step. +Let's take a look with examples step by step, starting from how lockdep +works without crossrelease for typical locks. + + acquire A /* Push A onto held_locks */ + acquire B /* Push B onto held_locks and add 'A -> B' */ + acquire C /* Push C onto held_locks and add 'B -> C' */ + release C /* Pop C from held_locks */ + release B /* Pop B from held_locks */ + release A /* Pop A from held_locks */ + + where A, B and C are different lock classes. + + NOTE: This document assumes that readers already understand how + lockdep works without crossrelease thus omits details. But there's + one thing to note. Lockdep pretends to pop a lock from held_locks + when releasing it. But it's subtly different from the original pop + operation because lockdep allows other than the top to be poped. + +In this case, lockdep adds 'the top of held_locks -> the lock to acquire' +dependency every time acquiring a lock. + +After adding 'A -> B', a dependency graph will be: + + A -> B + + where A and B are different lock classes. + +And after adding 'B -> C', the graph will be: + + A -> B -> C + + where A, B and C are different lock classes. + +Let's performs commit step even for typical locks to add dependencies. +Of course, commit step is not necessary for them, however, it would work +well because this is a more general way. + + acquire A + /* + * Queue A into hist_locks + * + * In hist_locks: A + * In graph: Empty + */ + + acquire B + /* + * Queue B into hist_locks + * + * In hist_locks: A, B + * In graph: Empty + */ + + acquire C + /* + * Queue C into hist_locks + * + * In hist_locks: A, B, C + * In graph: Empty + */ + + commit C + /* + * Add 'C -> ?' + * Answer the following to decide '?' + * What has been queued since acquire C: Nothing + * + * In hist_locks: A, B, C + * In graph: Empty + */ + + release C + + commit B + /* + * Add 'B -> ?' + * Answer the following to decide '?' + * What has been queued since acquire B: C + * + * In hist_locks: A, B, C + * In graph: 'B -> C' + */ + + release B + + commit A + /* + * Add 'A -> ?' + * Answer the following to decide '?' + * What has been queued since acquire A: B, C + * + * In hist_locks: A, B, C + * In graph: 'B -> C', 'A -> B', 'A -> C' + */ + + release A + + where A, B and C are different lock classes. + +In this case, dependencies are added at the commit step as described. + +After commits for A, B and C, the graph will be: + + A -> B -> C + + where A, B and C are different lock classes. + + NOTE: A dependency 'A -> C' is optimized out. + +We can see the former graph built without commit step is same as the +latter graph built using commit steps. Of course the former way leads to +earlier finish for building the graph, which means we can detect a +deadlock or its possibility sooner. So the former way would be prefered +when possible. But we cannot avoid using the latter way for crosslocks. + +Let's look at how commit steps work for crosslocks. In this case, the +commit step is performed only on crosslock AX as real. And it assumes +that the AX release context is different from the AX acquire context. + + BX RELEASE CONTEXT BX ACQUIRE CONTEXT + ------------------ ------------------ + acquire A + /* + * Push A onto held_locks + * Queue A into hist_locks + * + * In held_locks: A + * In hist_locks: A + * In graph: Empty + */ + + acquire BX + /* + * Add 'the top of held_locks -> BX' + * + * In held_locks: A + * In hist_locks: A + * In graph: 'A -> BX' + */ + + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + It must be guaranteed that the following operations are seen after + acquiring BX globally. It can be done by things like barrier. + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + + acquire C + /* + * Push C onto held_locks + * Queue C into hist_locks + * + * In held_locks: C + * In hist_locks: C + * In graph: 'A -> BX' + */ + + release C + /* + * Pop C from held_locks + * + * In held_locks: Empty + * In hist_locks: C + * In graph: 'A -> BX' + */ + acquire D + /* + * Push D onto held_locks + * Queue D into hist_locks + * Add 'the top of held_locks -> D' + * + * In held_locks: A, D + * In hist_locks: A, D + * In graph: 'A -> BX', 'A -> D' + */ + acquire E + /* + * Push E onto held_locks + * Queue E into hist_locks + * + * In held_locks: E + * In hist_locks: C, E + * In graph: 'A -> BX', 'A -> D' + */ + + release E + /* + * Pop E from held_locks + * + * In held_locks: Empty + * In hist_locks: D, E + * In graph: 'A -> BX', 'A -> D' + */ + release D + /* + * Pop D from held_locks + * + * In held_locks: A + * In hist_locks: A, D + * In graph: 'A -> BX', 'A -> D' + */ + commit BX + /* + * Add 'BX -> ?' + * What has been queued since acquire BX: C, E + * + * In held_locks: Empty + * In hist_locks: D, E + * In graph: 'A -> BX', 'A -> D', + * 'BX -> C', 'BX -> E' + */ + + release BX + /* + * In held_locks: Empty + * In hist_locks: D, E + * In graph: 'A -> BX', 'A -> D', + * 'BX -> C', 'BX -> E' + */ + release A + /* + * Pop A from held_locks + * + * In held_locks: Empty + * In hist_locks: A, D + * In graph: 'A -> BX', 'A -> D', + * 'BX -> C', 'BX -> E' + */ + + where A, BX, C,..., E are different lock classes, and a suffix 'X' is + added on crosslocks. + +Crossrelease considers all acquisitions after acqiuring BX are +candidates which might create dependencies with BX. True dependencies +will be determined when identifying the release context of BX. Meanwhile, +all typical locks are queued so that they can be used at the commit step. +And then two dependencies 'BX -> C' and 'BX -> E' are added at the +commit step when identifying the release context. + +The final graph will be, with crossrelease: + + -> C + / + -> BX - + / \ + A - -> E + \ + -> D + + where A, BX, C,..., E are different lock classes, and a suffix 'X' is + added on crosslocks. + +However, the final graph will be, without crossrelease: + + A -> D + + where A and D are different lock classes. + +The former graph has three more dependencies, 'A -> BX', 'BX -> C' and +'BX -> E' giving additional opportunities to check if they cause +deadlocks. This way lockdep can detect a deadlock or its possibility +caused by crosslocks. + +CONCLUSION + +We checked how crossrelease works with several examples. + + +============= +Optimizations +============= + +Avoid duplication +----------------- + +Crossrelease feature uses a cache like what lockdep already uses for +dependency chains, but this time it's for caching CT type dependencies. +Once that dependency is cached, the same will never be added again. + + +Lockless for hot paths +---------------------- + +To keep all locks for later use at the commit step, crossrelease adopts +a local array embedded in task_struct, which makes access to the data +lockless by forcing it to happen only within the owner context. It's +like how lockdep handles held_locks. Lockless implmentation is important +since typical locks are very frequently acquired and released. + + +================================================= +APPENDIX A: What lockdep does to work aggresively +================================================= + +A deadlock actually occurs when all wait operations creating circular +dependencies run at the same time. Even though they don't, a potential +deadlock exists if the problematic dependencies exist. Thus it's +meaningful to detect not only an actual deadlock but also its potential +possibility. The latter is rather valuable. When a deadlock occurs +actually, we can identify what happens in the system by some means or +other even without lockdep. However, there's no way to detect possiblity +without lockdep unless the whole code is parsed in head. It's terrible. +Lockdep does the both, and crossrelease only focuses on the latter. + +Whether or not a deadlock actually occurs depends on several factors. +For example, what order contexts are switched in is a factor. Assuming +circular dependencies exist, a deadlock would occur when contexts are +switched so that all wait operations creating the dependencies run +simultaneously. Thus to detect a deadlock possibility even in the case +that it has not occured yet, lockdep should consider all possible +combinations of dependencies, trying to: + +1. Use a global dependency graph. + + Lockdep combines all dependencies into one global graph and uses them, + regardless of which context generates them or what order contexts are + switched in. Aggregated dependencies are only considered so they are + prone to be circular if a problem exists. + +2. Check dependencies between classes instead of instances. + + What actually causes a deadlock are instances of lock. However, + lockdep checks dependencies between classes instead of instances. + This way lockdep can detect a deadlock which has not happened but + might happen in future by others but the same class. + +3. Assume all acquisitions lead to waiting. + + Although locks might be acquired without waiting which is essential + to create dependencies, lockdep assumes all acquisitions lead to + waiting since it might be true some time or another. + +CONCLUSION + +Lockdep detects not only an actual deadlock but also its possibility, +and the latter is more valuable. + + +================================================== +APPENDIX B: How to avoid adding false dependencies +================================================== + +Remind what a dependency is. A dependency exists if: + + 1. There are two waiters waiting for each event at a given time. + 2. The only way to wake up each waiter is to trigger its event. + 3. Whether one can be woken up depends on whether the other can. + +For example: + + acquire A + acquire B /* A dependency 'A -> B' exists */ + release B + release A + + where A and B are different lock classes. + +A depedency 'A -> B' exists since: + + 1. A waiter for A and a waiter for B might exist when acquiring B. + 2. Only way to wake up each is to release what it waits for. + 3. Whether the waiter for A can be woken up depends on whether the + other can. IOW, TASK X cannot release A if it fails to acquire B. + +For another example: + + TASK X TASK Y + ------ ------ + acquire AX + acquire B /* A dependency 'AX -> B' exists */ + release B + release AX held by Y + + where AX and B are different lock classes, and a suffix 'X' is added + on crosslocks. + +Even in this case involving crosslocks, the same rule can be applied. A +depedency 'AX -> B' exists since: + + 1. A waiter for AX and a waiter for B might exist when acquiring B. + 2. Only way to wake up each is to release what it waits for. + 3. Whether the waiter for AX can be woken up depends on whether the + other can. IOW, TASK X cannot release AX if it fails to acquire B. + +Let's take a look at more complicated example: + + TASK X TASK Y + ------ ------ + acquire B + release B + fork Y + acquire AX + acquire C /* A dependency 'AX -> C' exists */ + release C + release AX held by Y + + where AX, B and C are different lock classes, and a suffix 'X' is + added on crosslocks. + +Does a dependency 'AX -> B' exist? Nope. + +Two waiters are essential to create a dependency. However, waiters for +AX and B to create 'AX -> B' cannot exist at the same time in this +example. Thus the dependency 'AX -> B' cannot be created. + +It would be ideal if the full set of true ones can be considered. But +we can ensure nothing but what actually happened. Relying on what +actually happens at runtime, we can anyway add only true ones, though +they might be a subset of true ones. It's similar to how lockdep works +for typical locks. There might be more true dependencies than what +lockdep has detected in runtime. Lockdep has no choice but to rely on +what actually happens. Crossrelease also relies on it. + +CONCLUSION + +Relying on what actually happens, lockdep can avoid adding false +dependencies.
[toc] | [prev] | [next] | [standalone]
| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-08-07 09:20 +0200 |
| Subject | [PATCH v8 09/14] lockdep: Apply crossrelease to completions |
| Message-ID | <ubKuv-59V-37@gated-at.bofh.it> |
| In reply to | #1705149 |
Although wait_for_completion() and its family can cause deadlock, the
lock correctness validator could not be applied to them until now,
because things like complete() are usually called in a different context
from the waiting context, which violates lockdep's assumption.
Thanks to CONFIG_LOCKDEP_CROSSRELEASE, we can now apply the lockdep
detector to those completion operations. Applied it.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
include/linux/completion.h | 118 +++++++++++++++++++++++++++++++++++++++++----
kernel/sched/completion.c | 56 ++++++++++++---------
lib/Kconfig.debug | 8 +++
3 files changed, 149 insertions(+), 33 deletions(-)
diff --git a/include/linux/completion.h b/include/linux/completion.h
index 5d5aaae..6b3bcfc 100644
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -9,6 +9,9 @@
*/
#include <linux/wait.h>
+#ifdef CONFIG_LOCKDEP_COMPLETE
+#include <linux/lockdep.h>
+#endif
/*
* struct completion - structure used to maintain state for a "completion"
@@ -25,10 +28,50 @@
struct completion {
unsigned int done;
wait_queue_head_t wait;
+#ifdef CONFIG_LOCKDEP_COMPLETE
+ struct lockdep_map_cross map;
+#endif
};
+#ifdef CONFIG_LOCKDEP_COMPLETE
+static inline void complete_acquire(struct completion *x)
+{
+ lock_acquire_exclusive((struct lockdep_map *)&x->map, 0, 0, NULL, _RET_IP_);
+}
+
+static inline void complete_release(struct completion *x)
+{
+ lock_release((struct lockdep_map *)&x->map, 0, _RET_IP_);
+}
+
+static inline void complete_release_commit(struct completion *x)
+{
+ lock_commit_crosslock((struct lockdep_map *)&x->map);
+}
+
+#define init_completion(x) \
+do { \
+ static struct lock_class_key __key; \
+ lockdep_init_map_crosslock((struct lockdep_map *)&(x)->map, \
+ "(complete)" #x, \
+ &__key, 0); \
+ __init_completion(x); \
+} while (0)
+#else
+#define init_completion(x) __init_completion(x)
+static inline void complete_acquire(struct completion *x) {}
+static inline void complete_release(struct completion *x) {}
+static inline void complete_release_commit(struct completion *x) {}
+#endif
+
+#ifdef CONFIG_LOCKDEP_COMPLETE
+#define COMPLETION_INITIALIZER(work) \
+ { 0, __WAIT_QUEUE_HEAD_INITIALIZER((work).wait), \
+ STATIC_CROSS_LOCKDEP_MAP_INIT("(complete)" #work, &(work)) }
+#else
#define COMPLETION_INITIALIZER(work) \
{ 0, __WAIT_QUEUE_HEAD_INITIALIZER((work).wait) }
+#endif
#define COMPLETION_INITIALIZER_ONSTACK(work) \
({ init_completion(&work); work; })
@@ -70,7 +113,7 @@ struct completion {
* This inline function will initialize a dynamically created completion
* structure.
*/
-static inline void init_completion(struct completion *x)
+static inline void __init_completion(struct completion *x)
{
x->done = 0;
init_waitqueue_head(&x->wait);
@@ -88,18 +131,75 @@ static inline void reinit_completion(struct completion *x)
x->done = 0;
}
-extern void wait_for_completion(struct completion *);
-extern void wait_for_completion_io(struct completion *);
-extern int wait_for_completion_interruptible(struct completion *x);
-extern int wait_for_completion_killable(struct completion *x);
-extern unsigned long wait_for_completion_timeout(struct completion *x,
+extern void __wait_for_completion(struct completion *);
+extern void __wait_for_completion_io(struct completion *);
+extern int __wait_for_completion_interruptible(struct completion *x);
+extern int __wait_for_completion_killable(struct completion *x);
+extern unsigned long __wait_for_completion_timeout(struct completion *x,
unsigned long timeout);
-extern unsigned long wait_for_completion_io_timeout(struct completion *x,
+extern unsigned long __wait_for_completion_io_timeout(struct completion *x,
unsigned long timeout);
-extern long wait_for_completion_interruptible_timeout(
+extern long __wait_for_completion_interruptible_timeout(
struct completion *x, unsigned long timeout);
-extern long wait_for_completion_killable_timeout(
+extern long __wait_for_completion_killable_timeout(
struct completion *x, unsigned long timeout);
+
+static inline void wait_for_completion(struct completion *x)
+{
+ complete_acquire(x);
+ __wait_for_completion(x);
+ complete_release(x);
+}
+
+static inline void wait_for_completion_io(struct completion *x)
+{
+ complete_acquire(x);
+ __wait_for_completion_io(x);
+ complete_release(x);
+}
+
+static inline int wait_for_completion_interruptible(struct completion *x)
+{
+ int ret;
+ complete_acquire(x);
+ ret = __wait_for_completion_interruptible(x);
+ complete_release(x);
+ return ret;
+}
+
+static inline int wait_for_completion_killable(struct completion *x)
+{
+ int ret;
+ complete_acquire(x);
+ ret = __wait_for_completion_killable(x);
+ complete_release(x);
+ return ret;
+}
+
+static inline unsigned long wait_for_completion_timeout(struct completion *x,
+ unsigned long timeout)
+{
+ return __wait_for_completion_timeout(x, timeout);
+}
+
+static inline unsigned long wait_for_completion_io_timeout(struct completion *x,
+ unsigned long timeout)
+{
+ return __wait_for_completion_io_timeout(x, timeout);
+}
+
+static inline long wait_for_completion_interruptible_timeout(
+ struct completion *x, unsigned long timeout)
+{
+ return __wait_for_completion_interruptible_timeout(x, timeout);
+}
+
+static inline long wait_for_completion_killable_timeout(
+ struct completion *x, unsigned long timeout)
+{
+ return __wait_for_completion_killable_timeout(x, timeout);
+}
+
extern bool try_wait_for_completion(struct completion *x);
extern bool completion_done(struct completion *x);
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 13fc5ae..0b5f16b 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -32,6 +32,12 @@ void complete(struct completion *x)
unsigned long flags;
spin_lock_irqsave(&x->wait.lock, flags);
+
+ /*
+ * Perform commit of crossrelease here.
+ */
+ complete_release_commit(x);
+
if (x->done != UINT_MAX)
x->done++;
__wake_up_locked(&x->wait, TASK_NORMAL, 1);
@@ -111,7 +117,7 @@ void complete_all(struct completion *x)
}
/**
- * wait_for_completion: - waits for completion of a task
+ * __wait_for_completion: - waits for completion of a task
* @x: holds the state of this particular completion
*
* This waits to be signaled for completion of a specific task. It is NOT
@@ -120,14 +126,14 @@ void complete_all(struct completion *x)
* See also similar routines (i.e. wait_for_completion_timeout()) with timeout
* and interrupt capability. Also see complete().
*/
-void __sched wait_for_completion(struct completion *x)
+void __sched __wait_for_completion(struct completion *x)
{
wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
}
-EXPORT_SYMBOL(wait_for_completion);
+EXPORT_SYMBOL(__wait_for_completion);
/**
- * wait_for_completion_timeout: - waits for completion of a task (w/timeout)
+ * __wait_for_completion_timeout: - waits for completion of a task (w/timeout)
* @x: holds the state of this particular completion
* @timeout: timeout value in jiffies
*
@@ -139,28 +145,28 @@ void __sched wait_for_completion(struct completion *x)
* till timeout) if completed.
*/
unsigned long __sched
-wait_for_completion_timeout(struct completion *x, unsigned long timeout)
+__wait_for_completion_timeout(struct completion *x, unsigned long timeout)
{
return wait_for_common(x, timeout, TASK_UNINTERRUPTIBLE);
}
-EXPORT_SYMBOL(wait_for_completion_timeout);
+EXPORT_SYMBOL(__wait_for_completion_timeout);
/**
- * wait_for_completion_io: - waits for completion of a task
+ * __wait_for_completion_io: - waits for completion of a task
* @x: holds the state of this particular completion
*
* This waits to be signaled for completion of a specific task. It is NOT
* interruptible and there is no timeout. The caller is accounted as waiting
* for IO (which traditionally means blkio only).
*/
-void __sched wait_for_completion_io(struct completion *x)
+void __sched __wait_for_completion_io(struct completion *x)
{
wait_for_common_io(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
}
-EXPORT_SYMBOL(wait_for_completion_io);
+EXPORT_SYMBOL(__wait_for_completion_io);
/**
- * wait_for_completion_io_timeout: - waits for completion of a task (w/timeout)
+ * __wait_for_completion_io_timeout: - waits for completion of a task (w/timeout)
* @x: holds the state of this particular completion
* @timeout: timeout value in jiffies
*
@@ -173,14 +179,14 @@ void __sched wait_for_completion_io(struct completion *x)
* till timeout) if completed.
*/
unsigned long __sched
-wait_for_completion_io_timeout(struct completion *x, unsigned long timeout)
+__wait_for_completion_io_timeout(struct completion *x, unsigned long timeout)
{
return wait_for_common_io(x, timeout, TASK_UNINTERRUPTIBLE);
}
-EXPORT_SYMBOL(wait_for_completion_io_timeout);
+EXPORT_SYMBOL(__wait_for_completion_io_timeout);
/**
- * wait_for_completion_interruptible: - waits for completion of a task (w/intr)
+ * __wait_for_completion_interruptible: - waits for completion of a task (w/intr)
* @x: holds the state of this particular completion
*
* This waits for completion of a specific task to be signaled. It is
@@ -188,17 +194,18 @@ void __sched wait_for_completion_io(struct completion *x)
*
* Return: -ERESTARTSYS if interrupted, 0 if completed.
*/
-int __sched wait_for_completion_interruptible(struct completion *x)
+int __sched __wait_for_completion_interruptible(struct completion *x)
{
long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE);
+
if (t == -ERESTARTSYS)
return t;
return 0;
}
-EXPORT_SYMBOL(wait_for_completion_interruptible);
+EXPORT_SYMBOL(__wait_for_completion_interruptible);
/**
- * wait_for_completion_interruptible_timeout: - waits for completion (w/(to,intr))
+ * __wait_for_completion_interruptible_timeout: - waits for completion (w/(to,intr))
* @x: holds the state of this particular completion
* @timeout: timeout value in jiffies
*
@@ -209,15 +216,15 @@ int __sched wait_for_completion_interruptible(struct completion *x)
* or number of jiffies left till timeout) if completed.
*/
long __sched
-wait_for_completion_interruptible_timeout(struct completion *x,
+__wait_for_completion_interruptible_timeout(struct completion *x,
unsigned long timeout)
{
return wait_for_common(x, timeout, TASK_INTERRUPTIBLE);
}
-EXPORT_SYMBOL(wait_for_completion_interruptible_timeout);
+EXPORT_SYMBOL(__wait_for_completion_interruptible_timeout);
/**
- * wait_for_completion_killable: - waits for completion of a task (killable)
+ * __wait_for_completion_killable: - waits for completion of a task (killable)
* @x: holds the state of this particular completion
*
* This waits to be signaled for completion of a specific task. It can be
@@ -225,17 +232,18 @@ int __sched wait_for_completion_interruptible(struct completion *x)
*
* Return: -ERESTARTSYS if interrupted, 0 if completed.
*/
-int __sched wait_for_completion_killable(struct completion *x)
+int __sched __wait_for_completion_killable(struct completion *x)
{
long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_KILLABLE);
+
if (t == -ERESTARTSYS)
return t;
return 0;
}
-EXPORT_SYMBOL(wait_for_completion_killable);
+EXPORT_SYMBOL(__wait_for_completion_killable);
/**
- * wait_for_completion_killable_timeout: - waits for completion of a task (w/(to,killable))
+ * __wait_for_completion_killable_timeout: - waits for completion of a task (w/(to,killable))
* @x: holds the state of this particular completion
* @timeout: timeout value in jiffies
*
@@ -247,12 +255,12 @@ int __sched wait_for_completion_killable(struct completion *x)
* or number of jiffies left till timeout) if completed.
*/
long __sched
-wait_for_completion_killable_timeout(struct completion *x,
+__wait_for_completion_killable_timeout(struct completion *x,
unsigned long timeout)
{
return wait_for_common(x, timeout, TASK_KILLABLE);
}
-EXPORT_SYMBOL(wait_for_completion_killable_timeout);
+EXPORT_SYMBOL(__wait_for_completion_killable_timeout);
/**
* try_wait_for_completion - try to decrement a completion without blocking
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 037e813..4ba8adc 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1085,6 +1085,14 @@ config LOCKDEP_CROSSRELEASE
such as page locks or completions can use the lock correctness
detector, lockdep.
+config LOCKDEP_COMPLETE
+ bool "Lock debugging: allow completions to use deadlock detector"
+ select LOCKDEP_CROSSRELEASE
+ default n
+ help
+ A deadlock caused by wait_for_completion() and complete() can be
+ detected by lockdep using crossrelease feature.
+
config PROVE_LOCKING
bool "Lock debugging: prove locking correctness"
depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
--
1.9.1
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| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Date | 2017-08-09 12:00 +0200 |
| Subject | Re: [PATCH v8 09/14] lockdep: Apply crossrelease to completions |
| Message-ID | <ucvWr-5qB-15@gated-at.bofh.it> |
| In reply to | #1705160 |
On Mon, Aug 07, 2017 at 04:12:56PM +0900, Byungchul Park wrote:
> +static inline void wait_for_completion(struct completion *x)
> +{
> + complete_acquire(x);
> + __wait_for_completion(x);
> + complete_release(x);
> +}
> +
> +static inline void wait_for_completion_io(struct completion *x)
> +{
> + complete_acquire(x);
> + __wait_for_completion_io(x);
> + complete_release(x);
> +}
> +
> +static inline int wait_for_completion_interruptible(struct completion *x)
> +{
> + int ret;
> + complete_acquire(x);
> + ret = __wait_for_completion_interruptible(x);
> + complete_release(x);
> + return ret;
> +}
> +
> +static inline int wait_for_completion_killable(struct completion *x)
> +{
> + int ret;
> + complete_acquire(x);
> + ret = __wait_for_completion_killable(x);
> + complete_release(x);
> + return ret;
> +}
I don't understand, why not change __wait_for_common() ?
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| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Date | 2017-08-09 12:30 +0200 |
| Subject | Re: [PATCH v8 09/14] lockdep: Apply crossrelease to completions |
| Message-ID | <ucwpr-5Qr-1@gated-at.bofh.it> |
| In reply to | #1707210 |
On Wed, Aug 09, 2017 at 11:51:07AM +0200, Peter Zijlstra wrote:
> On Mon, Aug 07, 2017 at 04:12:56PM +0900, Byungchul Park wrote:
> > +static inline void wait_for_completion(struct completion *x)
> > +{
> > + complete_acquire(x);
> > + __wait_for_completion(x);
> > + complete_release(x);
> > +}
> > +
> > +static inline void wait_for_completion_io(struct completion *x)
> > +{
> > + complete_acquire(x);
> > + __wait_for_completion_io(x);
> > + complete_release(x);
> > +}
> > +
> > +static inline int wait_for_completion_interruptible(struct completion *x)
> > +{
> > + int ret;
> > + complete_acquire(x);
> > + ret = __wait_for_completion_interruptible(x);
> > + complete_release(x);
> > + return ret;
> > +}
> > +
> > +static inline int wait_for_completion_killable(struct completion *x)
> > +{
> > + int ret;
> > + complete_acquire(x);
> > + ret = __wait_for_completion_killable(x);
> > + complete_release(x);
> > + return ret;
> > +}
>
> I don't understand, why not change __wait_for_common() ?
That is what is wrong with the below?
Yes, it adds acquire/release to the timeout variants too, but I don't
see why we should exclude those, and even if we'd want to do that, it
would be trivial:
bool timo = (timeout == MAX_SCHEDULE_TIMEOUT);
if (!timo)
complete_acquire(x);
/* ... */
if (!timo)
complete_release(x);
But like said, I think we very much want to annotate waits with timeouts
too. Hitting the max timo doesn't necessarily mean we'll make fwd
progress, we could be stuck in a loop doing something else again before
returning to wait.
Also, even if we'd make fwd progress, hitting that max timo is still not
desirable.
---
Subject: lockdep: Apply crossrelease to completions
From: Byungchul Park <byungchul.park@lge.com>
Date: Mon, 7 Aug 2017 16:12:56 +0900
Although wait_for_completion() and its family can cause deadlock, the
lock correctness validator could not be applied to them until now,
because things like complete() are usually called in a different context
from the waiting context, which violates lockdep's assumption.
Thanks to CONFIG_LOCKDEP_CROSSRELEASE, we can now apply the lockdep
detector to those completion operations. Applied it.
Cc: npiggin@gmail.com
Cc: mingo@kernel.org
Cc: akpm@linux-foundation.org
Cc: tglx@linutronix.de
Cc: boqun.feng@gmail.com
Cc: willy@infradead.org
Cc: walken@google.com
Cc: kernel-team@lge.com
Cc: kirill@shutemov.name
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/completion.h | 45 ++++++++++++++++++++++++++++++++++++++++++++-
kernel/sched/completion.c | 11 +++++++++++
lib/Kconfig.debug | 8 ++++++++
3 files changed, 63 insertions(+), 1 deletion(-)
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -9,6 +9,9 @@
*/
#include <linux/wait.h>
+#ifdef CONFIG_LOCKDEP_COMPLETE
+#include <linux/lockdep.h>
+#endif
/*
* struct completion - structure used to maintain state for a "completion"
@@ -25,10 +28,50 @@
struct completion {
unsigned int done;
wait_queue_head_t wait;
+#ifdef CONFIG_LOCKDEP_COMPLETE
+ struct lockdep_map_cross map;
+#endif
};
+#ifdef CONFIG_LOCKDEP_COMPLETE
+static inline void complete_acquire(struct completion *x)
+{
+ lock_acquire_exclusive((struct lockdep_map *)&x->map, 0, 0, NULL, _RET_IP_);
+}
+
+static inline void complete_release(struct completion *x)
+{
+ lock_release((struct lockdep_map *)&x->map, 0, _RET_IP_);
+}
+
+static inline void complete_release_commit(struct completion *x)
+{
+ lock_commit_crosslock((struct lockdep_map *)&x->map);
+}
+
+#define init_completion(x) \
+do { \
+ static struct lock_class_key __key; \
+ lockdep_init_map_crosslock((struct lockdep_map *)&(x)->map, \
+ "(complete)" #x, \
+ &__key, 0); \
+ __init_completion(x); \
+} while (0)
+#else
+#define init_completion(x) __init_completion(x)
+static inline void complete_acquire(struct completion *x) {}
+static inline void complete_release(struct completion *x) {}
+static inline void complete_release_commit(struct completion *x) {}
+#endif
+
+#ifdef CONFIG_LOCKDEP_COMPLETE
+#define COMPLETION_INITIALIZER(work) \
+ { 0, __WAIT_QUEUE_HEAD_INITIALIZER((work).wait), \
+ STATIC_CROSS_LOCKDEP_MAP_INIT("(complete)" #work, &(work)) }
+#else
#define COMPLETION_INITIALIZER(work) \
{ 0, __WAIT_QUEUE_HEAD_INITIALIZER((work).wait) }
+#endif
#define COMPLETION_INITIALIZER_ONSTACK(work) \
({ init_completion(&work); work; })
@@ -70,7 +113,7 @@ struct completion {
* This inline function will initialize a dynamically created completion
* structure.
*/
-static inline void init_completion(struct completion *x)
+static inline void __init_completion(struct completion *x)
{
x->done = 0;
init_waitqueue_head(&x->wait);
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -32,6 +32,12 @@ void complete(struct completion *x)
unsigned long flags;
spin_lock_irqsave(&x->wait.lock, flags);
+
+ /*
+ * Perform commit of crossrelease here.
+ */
+ complete_release_commit(x);
+
if (x->done != UINT_MAX)
x->done++;
__wake_up_locked(&x->wait, TASK_NORMAL, 1);
@@ -92,9 +98,14 @@ __wait_for_common(struct completion *x,
{
might_sleep();
+ complete_acquire(x);
+
spin_lock_irq(&x->wait.lock);
timeout = do_wait_for_common(x, action, timeout, state);
spin_unlock_irq(&x->wait.lock);
+
+ complete_release(x);
+
return timeout;
}
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1085,6 +1085,14 @@ config LOCKDEP_CROSSRELEASE
such as page locks or completions can use the lock correctness
detector, lockdep.
+config LOCKDEP_COMPLETE
+ bool "Lock debugging: allow completions to use deadlock detector"
+ select LOCKDEP_CROSSRELEASE
+ default n
+ help
+ A deadlock caused by wait_for_completion() and complete() can be
+ detected by lockdep using crossrelease feature.
+
config PROVE_LOCKING
bool "Lock debugging: prove locking correctness"
depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
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