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| Started by | Davidlohr Bueso <dave@stgolabs.net> |
|---|---|
| First post | 2016-02-09 20:20 +0100 |
| Last post | 2016-02-17 13:30 +0100 |
| Articles | 3 — 2 participants |
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[PATCH v6 0/2] futex: lockless get_futex_key Davidlohr Bueso <dave@stgolabs.net> - 2016-02-09 20:20 +0100
[PATCH v6 1/2] futex: Rename barrier references in ordering guarantees Davidlohr Bueso <dave@stgolabs.net> - 2016-02-09 20:20 +0100
[tip:locking/core] futex: Rename barrier references in ordering guarantees tip-bot for Davidlohr Bueso <tipbot@zytor.com> - 2016-02-17 13:30 +0100
| From | Davidlohr Bueso <dave@stgolabs.net> |
|---|---|
| Date | 2016-02-09 20:20 +0100 |
| Subject | [PATCH v6 0/2] futex: lockless get_futex_key |
| Message-ID | <r0lZo-8lW-7@gated-at.bofh.it> |
This is the continuation of the original patch, except with Ingo's
feedback about the ordering comments we have and how we reference
them throughout the code. Please consider for v4.6.
Thanks!
Changes from v5:
- Added patch 1 (Ingo).
Changes from v4:
- Integrated feedback from Hugh, specifically:
* check for page->mapping change with page lock held when
detecting shm race.
* move inode assign, if the mapping still matches what
we expect should we have a valid inode.
* move iput out of rcu lock.
Changes from v3:
- Redo mapping sanity check, now do not halt the kernel.
Changes from v2:
- Minor adjustments by peterz.
- Applies on top of -next-20160118
Changes from v1:
- Remove unnecesary mb, as atomic_inc returning does what we need.
- Fix bogus mapping load.
- Minor code cleanups/comments.
Davidlohr Bueso (2):
futex: Rename barrier references in ordering guarantees
futex: Remove requirement for lock_page in get_futex_key
kernel/futex.c | 131 ++++++++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 107 insertions(+), 24 deletions(-)
--
2.1.4
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| From | Davidlohr Bueso <dave@stgolabs.net> |
|---|---|
| Date | 2016-02-09 20:20 +0100 |
| Subject | [PATCH v6 1/2] futex: Rename barrier references in ordering guarantees |
| Message-ID | <r0lZo-8lW-11@gated-at.bofh.it> |
| In reply to | #1330597 |
Ingo suggested we rename how we reference barriers A and B
regarding futex ordering guarantees. This patch replaces,
for both barriers, MB (A) with smp_mb(); (A), such that:
- We explicitly state that the barriers are SMP, and
- We standardize how we reference these across futex.c
helping readers follow what barrier does what and where.
Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
kernel/futex.c | 34 +++++++++++++++++-----------------
1 file changed, 17 insertions(+), 17 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index 5d6ce64..08ac700 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -124,16 +124,16 @@
* futex_wait(futex, val);
*
* waiters++; (a)
- * mb(); (A) <-- paired with -.
- * |
- * lock(hash_bucket(futex)); |
- * |
- * uval = *futex; |
- * | *futex = newval;
- * | sys_futex(WAKE, futex);
- * | futex_wake(futex);
- * |
- * `-------> mb(); (B)
+ * smp_mb(); (A) <-- paired with -.
+ * |
+ * lock(hash_bucket(futex)); |
+ * |
+ * uval = *futex; |
+ * | *futex = newval;
+ * | sys_futex(WAKE, futex);
+ * | futex_wake(futex);
+ * |
+ * `--------> smp_mb(); (B)
* if (uval == val)
* queue();
* unlock(hash_bucket(futex));
@@ -334,7 +334,7 @@ static inline void futex_get_mm(union futex_key *key)
/*
* Ensure futex_get_mm() implies a full barrier such that
* get_futex_key() implies a full barrier. This is relied upon
- * as full barrier (B), see the ordering comment above.
+ * as smp_mb(); (B), see the ordering comment above.
*/
smp_mb__after_atomic();
}
@@ -407,10 +407,10 @@ static void get_futex_key_refs(union futex_key *key)
switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
case FUT_OFF_INODE:
- ihold(key->shared.inode); /* implies MB (B) */
+ ihold(key->shared.inode); /* implies smp_mb(); (B) */
break;
case FUT_OFF_MMSHARED:
- futex_get_mm(key); /* implies MB (B) */
+ futex_get_mm(key); /* implies smp_mb(); (B) */
break;
default:
/*
@@ -418,7 +418,7 @@ static void get_futex_key_refs(union futex_key *key)
* mm, therefore the only purpose of calling get_futex_key_refs
* is because we need the barrier for the lockless waiter check.
*/
- smp_mb(); /* explicit MB (B) */
+ smp_mb(); /* explicit smp_mb(); (B) */
}
}
@@ -497,7 +497,7 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
if (!fshared) {
key->private.mm = mm;
key->private.address = address;
- get_futex_key_refs(key); /* implies MB (B) */
+ get_futex_key_refs(key); /* implies smp_mb(); (B) */
return 0;
}
@@ -572,7 +572,7 @@ again:
key->shared.pgoff = basepage_index(page);
}
- get_futex_key_refs(key); /* implies MB (B) */
+ get_futex_key_refs(key); /* implies smp_mb(); (B) */
out:
unlock_page(page);
@@ -1864,7 +1864,7 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
q->lock_ptr = &hb->lock;
- spin_lock(&hb->lock); /* implies MB (A) */
+ spin_lock(&hb->lock); /* implies smp_mb(); (A) */
return hb;
}
--
2.1.4
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| From | tip-bot for Davidlohr Bueso <tipbot@zytor.com> |
|---|---|
| Date | 2016-02-17 13:30 +0100 |
| Subject | [tip:locking/core] futex: Rename barrier references in ordering guarantees |
| Message-ID | <r39p3-6nX-77@gated-at.bofh.it> |
| In reply to | #1330598 |
Commit-ID: 8ad7b378d0d016309014cae0f640434bca7b5e11
Gitweb: http://git.kernel.org/tip/8ad7b378d0d016309014cae0f640434bca7b5e11
Author: Davidlohr Bueso <dave@stgolabs.net>
AuthorDate: Tue, 9 Feb 2016 11:15:13 -0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 17 Feb 2016 10:42:17 +0100
futex: Rename barrier references in ordering guarantees
Ingo suggested we rename how we reference barriers A and B
regarding futex ordering guarantees. This patch replaces,
for both barriers, MB (A) with smp_mb(); (A), such that:
- We explicitly state that the barriers are SMP, and
- We standardize how we reference these across futex.c
helping readers follow what barrier does what and where.
Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Mason <clm@fb.com>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: dave@stgolabs.net
Link: http://lkml.kernel.org/r/1455045314-8305-2-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/futex.c | 34 +++++++++++++++++-----------------
1 file changed, 17 insertions(+), 17 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index 5d6ce64..08ac700 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -124,16 +124,16 @@
* futex_wait(futex, val);
*
* waiters++; (a)
- * mb(); (A) <-- paired with -.
- * |
- * lock(hash_bucket(futex)); |
- * |
- * uval = *futex; |
- * | *futex = newval;
- * | sys_futex(WAKE, futex);
- * | futex_wake(futex);
- * |
- * `-------> mb(); (B)
+ * smp_mb(); (A) <-- paired with -.
+ * |
+ * lock(hash_bucket(futex)); |
+ * |
+ * uval = *futex; |
+ * | *futex = newval;
+ * | sys_futex(WAKE, futex);
+ * | futex_wake(futex);
+ * |
+ * `--------> smp_mb(); (B)
* if (uval == val)
* queue();
* unlock(hash_bucket(futex));
@@ -334,7 +334,7 @@ static inline void futex_get_mm(union futex_key *key)
/*
* Ensure futex_get_mm() implies a full barrier such that
* get_futex_key() implies a full barrier. This is relied upon
- * as full barrier (B), see the ordering comment above.
+ * as smp_mb(); (B), see the ordering comment above.
*/
smp_mb__after_atomic();
}
@@ -407,10 +407,10 @@ static void get_futex_key_refs(union futex_key *key)
switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
case FUT_OFF_INODE:
- ihold(key->shared.inode); /* implies MB (B) */
+ ihold(key->shared.inode); /* implies smp_mb(); (B) */
break;
case FUT_OFF_MMSHARED:
- futex_get_mm(key); /* implies MB (B) */
+ futex_get_mm(key); /* implies smp_mb(); (B) */
break;
default:
/*
@@ -418,7 +418,7 @@ static void get_futex_key_refs(union futex_key *key)
* mm, therefore the only purpose of calling get_futex_key_refs
* is because we need the barrier for the lockless waiter check.
*/
- smp_mb(); /* explicit MB (B) */
+ smp_mb(); /* explicit smp_mb(); (B) */
}
}
@@ -497,7 +497,7 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
if (!fshared) {
key->private.mm = mm;
key->private.address = address;
- get_futex_key_refs(key); /* implies MB (B) */
+ get_futex_key_refs(key); /* implies smp_mb(); (B) */
return 0;
}
@@ -572,7 +572,7 @@ again:
key->shared.pgoff = basepage_index(page);
}
- get_futex_key_refs(key); /* implies MB (B) */
+ get_futex_key_refs(key); /* implies smp_mb(); (B) */
out:
unlock_page(page);
@@ -1864,7 +1864,7 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
q->lock_ptr = &hb->lock;
- spin_lock(&hb->lock); /* implies MB (A) */
+ spin_lock(&hb->lock); /* implies smp_mb(); (A) */
return hb;
}
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