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[RFC tip/locking v2 00/13] lockdep: Support deadlock detection for recursive read locks

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  [RFC tip/locking v2 00/13] lockdep: Support deadlock detection for recursive read locks Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:30 +0200
    [RFC tip/locking v2 01/13] lockdep: Demagic the return value of BFS Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:30 +0200
    [RFC tip/locking v2 08/13] lockdep: Fix recursive read lock related safe->unsafe detection Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 12/13] lockdep/selftest: Unleash irq_read_recursion2 and add more Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 07/13] lockdep: Support deadlock detection for recursive read in check_noncircular() Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 13/13] lockdep/selftest: Add more recursive read related test cases Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 03/13] lockdep: Change the meanings of LOCK_{USED_IN, ENABLED}_*_{READ} Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 04/13] lockdep: Introduce lock_list::dep Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 05/13] lockdep: Extend __bfs() to work with multiple kinds of dependencies Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 09/13] lockdep: Add recursive read locks into dependency graph Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 11/13] lockdep: Take read/write status in consideration when generate chainkey Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 02/13] lockdep: Make __bfs() visit every dependency rather than every class until a match Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 06/13] lockdep: Adjust check_redundant() for recursive read change Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    [RFC tip/locking v2 10/13] lockdep/selftest: Add a R-L/L-W test case specific to chain cache behavior Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:40 +0200
    Re: [RFC tip/locking v2 00/13] lockdep: Support deadlock detection  for recursive read locks Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 10:50 +0200

#1727213 — [RFC tip/locking v2 00/13] lockdep: Support deadlock detection for recursive read locks

Hi Ingo and Peter,

This is V2 for recursive read lock support in lockdep. I fix several
bugs in V1 and also add irq inversion detection support for recursive
read locks.

V1: https://marc.info/?l=linux-kernel&m=150393341825453


As Peter pointed out:

	https://marc.info/?l=linux-kernel&m=150349072023540

The lockdep current has a limit support for recursive read locks, the
deadlock case as follow could not be detected:

	read_lock(A);
				lock(B);
	lock(B);
				write_lock(A);

I got some inspiration from Gautham R Shenoy:

	https://lwn.net/Articles/332801/

, and came up with this series.

The basic idea is:

*	Add recursive read locks into the graph

*	Classify dependencies into --(RR)-->, --(NR)-->, --(RN)-->,
	--(NN)-->, where R stands for recursive read lock, N stands for
	other locks(i.e. non-recursive read locks and write locks).

*	Define strong dependency paths as the paths of dependencies
	don't have two adjacent dependencies as --(*R)--> and --(R*)-->.

*	Extend __bfs() to only traverse on strong dependency paths.

*	If __bfs() finds a strong dependency circle, then a deadlock is
	reported.

The whole series is based on current master branch of Linus' tree:

	e7d0c41ecc2e ("Merge tag 'devprop-4.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm")

, and I also put it at:

	git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git arr-rfc-v2

The whole series consists of 13 patches:

1.	Do a clean up on the return value of __bfs() and its friends.

2.	Make __bfs() able to visit every dependency until a match is
	found. The old version of __bfs() could only visit each lock
	class once, and this is insufficient if we are going to add
	recursive read locks into the dependency graph.

3.	Make lock state LOCK_*_READ stand for recursive read lock only
	and LOCK_* stand for write lock and non-recursive read lock.

4-5	Extend __bfs() to be able to traverse the stong dependency
	patchs after recursive read locks added into the graph.

6-8	Adjust check_redundant(), check_noncircular() and
	check_irq_usage() with recursive read locks into consideration.

9.	Finally add recursive read locks into the dependency graph.

10-11	Adjust lock cache chain key generation with recursive read locks
	into consideration, and provide a test case.

12-13	Add more test cases.

I did pass all the lockdep selftest cases(including those I introduce),
and now run it on one of my box, haven't shot my feet yet.

Test and comments are welcome!

Regards,
Boqun

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#1727218 — [RFC tip/locking v2 01/13] lockdep: Demagic the return value of BFS

__bfs() could return four magic numbers:

	1: search succeeds, but none match.
	0: search succeeds, find one match.
	-1: search fails because of the cq is full.
	-2: search fails because a invalid node is found.

This patch cleans things up by making a enum type for the return value
of __bfs() and its friends, this improves the code readability of the
code, and further, could help if we want to extend the BFS.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/locking/lockdep.c | 134 ++++++++++++++++++++++++++++-------------------
 1 file changed, 79 insertions(+), 55 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 44c8d0d17170..df0b7e620659 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -996,21 +996,52 @@ static inline int get_lock_depth(struct lock_list *child)
 	}
 	return depth;
 }
+/*
+ * Return values of a bfs search:
+ *
+ * BFS_E* indicates an error
+ * BFS_R* indicates a result(match or not)
+ *
+ * BFS_EINVALIDNODE: Find a invalid node in the graph.
+ *
+ * BFS_EQUEUEFULL: The queue is full while doing the bfs.
+ *
+ * BFS_RMATCH: Find the matched node in the graph, and put that node * into
+ *            *@target_entry.
+ *
+ * BFS_RNOMATCH: Haven't found the matched node and keep *@target_entry
+ *              _unchanged_.
+ */
+enum bfs_result {
+	BFS_EINVALIDNODE = -2,
+	BFS_EQUEUEFULL = -1,
+	BFS_RMATCH = 0,
+	BFS_RNOMATCH = 1,
+};
+
+/*
+ * bfs_result < 0 means error
+ */
+
+static inline bool bfs_error(enum bfs_result res)
+{
+	return res < 0;
+}
 
-static int __bfs(struct lock_list *source_entry,
-		 void *data,
-		 int (*match)(struct lock_list *entry, void *data),
-		 struct lock_list **target_entry,
-		 int forward)
+static enum bfs_result __bfs(struct lock_list *source_entry,
+			     void *data,
+			     int (*match)(struct lock_list *entry, void *data),
+			     struct lock_list **target_entry,
+			     int forward)
 {
 	struct lock_list *entry;
 	struct list_head *head;
 	struct circular_queue *cq = &lock_cq;
-	int ret = 1;
+	enum bfs_result ret = BFS_RNOMATCH;
 
 	if (match(source_entry, data)) {
 		*target_entry = source_entry;
-		ret = 0;
+		ret = BFS_RMATCH;
 		goto exit;
 	}
 
@@ -1031,7 +1062,7 @@ static int __bfs(struct lock_list *source_entry,
 		__cq_dequeue(cq, (unsigned long *)&lock);
 
 		if (!lock->class) {
-			ret = -2;
+			ret = BFS_EINVALIDNODE;
 			goto exit;
 		}
 
@@ -1048,12 +1079,12 @@ static int __bfs(struct lock_list *source_entry,
 				mark_lock_accessed(entry, lock);
 				if (match(entry, data)) {
 					*target_entry = entry;
-					ret = 0;
+					ret = BFS_RMATCH;
 					goto exit;
 				}
 
 				if (__cq_enqueue(cq, (unsigned long)entry)) {
-					ret = -1;
+					ret = BFS_EQUEUEFULL;
 					goto exit;
 				}
 				cq_depth = __cq_get_elem_count(cq);
@@ -1066,19 +1097,21 @@ static int __bfs(struct lock_list *source_entry,
 	return ret;
 }
 
-static inline int __bfs_forwards(struct lock_list *src_entry,
-			void *data,
-			int (*match)(struct lock_list *entry, void *data),
-			struct lock_list **target_entry)
+static inline enum bfs_result
+__bfs_forwards(struct lock_list *src_entry,
+	       void *data,
+	       int (*match)(struct lock_list *entry, void *data),
+	       struct lock_list **target_entry)
 {
 	return __bfs(src_entry, data, match, target_entry, 1);
 
 }
 
-static inline int __bfs_backwards(struct lock_list *src_entry,
-			void *data,
-			int (*match)(struct lock_list *entry, void *data),
-			struct lock_list **target_entry)
+static inline enum bfs_result
+__bfs_backwards(struct lock_list *src_entry,
+		void *data,
+		int (*match)(struct lock_list *entry, void *data),
+		struct lock_list **target_entry)
 {
 	return __bfs(src_entry, data, match, target_entry, 0);
 
@@ -1335,13 +1368,13 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
 
 /*
  * Prove that the dependency graph starting at <entry> can not
- * lead to <target>. Print an error and return 0 if it does.
+ * lead to <target>. Print an error and return BFS_RMATCH if it does.
  */
-static noinline int
+static noinline enum bfs_result
 check_noncircular(struct lock_list *root, struct lock_class *target,
-		struct lock_list **target_entry)
+		  struct lock_list **target_entry)
 {
-	int result;
+	enum bfs_result result;
 
 	debug_atomic_inc(nr_cyclic_checks);
 
@@ -1350,11 +1383,11 @@ check_noncircular(struct lock_list *root, struct lock_class *target,
 	return result;
 }
 
-static noinline int
+static noinline enum bfs_result
 check_redundant(struct lock_list *root, struct lock_class *target,
 		struct lock_list **target_entry)
 {
-	int result;
+	enum bfs_result result;
 
 	debug_atomic_inc(nr_redundant_checks);
 
@@ -1383,15 +1416,12 @@ static inline int usage_match(struct lock_list *entry, void *bit)
  *
  * Return 0 if such a node exists in the subgraph, and put that node
  * into *@target_entry.
- *
- * Return 1 otherwise and keep *@target_entry unchanged.
- * Return <0 on error.
  */
-static int
+static enum bfs_result
 find_usage_forwards(struct lock_list *root, enum lock_usage_bit bit,
 			struct lock_list **target_entry)
 {
-	int result;
+	enum bfs_result result;
 
 	debug_atomic_inc(nr_find_usage_forwards_checks);
 
@@ -1403,18 +1433,12 @@ find_usage_forwards(struct lock_list *root, enum lock_usage_bit bit,
 /*
  * Find a node in the backwards-direction dependency sub-graph starting
  * at @root->class that matches @bit.
- *
- * Return 0 if such a node exists in the subgraph, and put that node
- * into *@target_entry.
- *
- * Return 1 otherwise and keep *@target_entry unchanged.
- * Return <0 on error.
  */
-static int
+static enum bfs_result
 find_usage_backwards(struct lock_list *root, enum lock_usage_bit bit,
 			struct lock_list **target_entry)
 {
-	int result;
+	enum bfs_result result;
 
 	debug_atomic_inc(nr_find_usage_backwards_checks);
 
@@ -1622,18 +1646,18 @@ check_usage(struct task_struct *curr, struct held_lock *prev,
 
 	this.class = hlock_class(prev);
 	ret = find_usage_backwards(&this, bit_backwards, &target_entry);
-	if (ret < 0)
+	if (bfs_error(ret))
 		return print_bfs_bug(ret);
-	if (ret == 1)
-		return ret;
+	if (ret == BFS_RNOMATCH)
+		return 1;
 
 	that.parent = NULL;
 	that.class = hlock_class(next);
 	ret = find_usage_forwards(&that, bit_forwards, &target_entry1);
-	if (ret < 0)
+	if (bfs_error(ret))
 		return print_bfs_bug(ret);
-	if (ret == 1)
-		return ret;
+	if (ret == BFS_RNOMATCH)
+		return 1;
 
 	return print_bad_irq_dependency(curr, &this, &that,
 			target_entry, target_entry1,
@@ -1874,7 +1898,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	       int (*save)(struct stack_trace *trace))
 {
 	struct lock_list *entry;
-	int ret;
+	enum bfs_result ret;
 	struct lock_list this;
 	struct lock_list *uninitialized_var(target_entry);
 
@@ -1890,9 +1914,9 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	this.class = hlock_class(next);
 	this.parent = NULL;
 	ret = check_noncircular(&this, hlock_class(prev), &target_entry);
-	if (unlikely(!ret))
+	if (unlikely(ret == BFS_RMATCH))
 		return print_circular_bug(&this, target_entry, next, prev, trace);
-	else if (unlikely(ret < 0))
+	else if (unlikely(bfs_error(ret)))
 		return print_bfs_bug(ret);
 
 	if (!check_prev_add_irq(curr, prev, next))
@@ -1930,11 +1954,11 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	this.class = hlock_class(prev);
 	this.parent = NULL;
 	ret = check_redundant(&this, hlock_class(next), &target_entry);
-	if (!ret) {
+	if (ret == BFS_RMATCH) {
 		debug_atomic_inc(nr_redundant);
 		return 2;
 	}
-	if (ret < 0)
+	if (bfs_error(ret))
 		return print_bfs_bug(ret);
 
 
@@ -2685,16 +2709,16 @@ static int
 check_usage_forwards(struct task_struct *curr, struct held_lock *this,
 		     enum lock_usage_bit bit, const char *irqclass)
 {
-	int ret;
+	enum bfs_result ret;
 	struct lock_list root;
 	struct lock_list *uninitialized_var(target_entry);
 
 	root.parent = NULL;
 	root.class = hlock_class(this);
 	ret = find_usage_forwards(&root, bit, &target_entry);
-	if (ret < 0)
+	if (bfs_error(ret))
 		return print_bfs_bug(ret);
-	if (ret == 1)
+	if (ret == BFS_RNOMATCH)
 		return ret;
 
 	return print_irq_inversion_bug(curr, &root, target_entry,
@@ -2709,17 +2733,17 @@ static int
 check_usage_backwards(struct task_struct *curr, struct held_lock *this,
 		      enum lock_usage_bit bit, const char *irqclass)
 {
-	int ret;
+	enum bfs_result ret;
 	struct lock_list root;
 	struct lock_list *uninitialized_var(target_entry);
 
 	root.parent = NULL;
 	root.class = hlock_class(this);
 	ret = find_usage_backwards(&root, bit, &target_entry);
-	if (ret < 0)
+	if (bfs_error(ret))
 		return print_bfs_bug(ret);
-	if (ret == 1)
-		return ret;
+	if (ret == BFS_RNOMATCH)
+		return 1;
 
 	return print_irq_inversion_bug(curr, &root, target_entry,
 					this, 0, irqclass);
-- 
2.14.1

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#1727221 — [RFC tip/locking v2 08/13] lockdep: Fix recursive read lock related safe->unsafe detection

There are four cases for recursive read lock realted deadlocks:

(--(X..Y)--> means a strong dependency path starts with a --(X*)-->
dependency and ends with a --(*Y)-- dependency.)

1.	An irq-safe lock L1 has a dependency --(*..*)--> to an
	irq-unsafe lock L2.

2.	An irq-read-safe lock L1 has a dependency --(N..*)--> to an
	irq-unsafe lock L2.

3.	An irq-safe lock L1 has a dependency --(*..N)--> to an
	irq-read-unsafe lock L2.

4.	An irq-read-safe lock L1 has a dependency --(N..N)--> to an
	irq-read-unsafe lock L2.

The current check_usage() only checks 1) and 2), so this patch adds
checks for 3) and 4) and makes sure when find_usage_{back,for}wards find
an irq-read-{,un}safe lock, the traverse path should ends at a
dependency --(*N)-->. Note when we search backwards, --(*N)--> indicates
a real dependency --(N*)-->.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/locking/lockdep.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 8a09b1a02342..6659b91b70f2 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1505,7 +1505,14 @@ check_redundant(struct lock_list *root, struct held_lock *target,
 
 static inline int usage_match(struct lock_list *entry, void *bit)
 {
-	return entry->class->usage_mask & (1 << (enum lock_usage_bit)bit);
+	enum lock_usage_bit ub = (enum lock_usage_bit)bit;
+
+
+	if (ub & 1)
+		return entry->class->usage_mask & (1 << ub) &&
+		       !entry->is_rr;
+	else
+		return entry->class->usage_mask & (1 << ub);
 }
 
 
@@ -1816,6 +1823,10 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
 			   exclusive_bit(bit), state_name(bit)))
 		return 0;
 
+	if (!check_usage(curr, prev, next, bit,
+			   exclusive_bit(bit) + 1, state_name(bit)))
+		return 0;
+
 	bit++; /* _READ */
 
 	/*
@@ -1828,6 +1839,10 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
 			   exclusive_bit(bit), state_name(bit)))
 		return 0;
 
+	if (!check_usage(curr, prev, next, bit,
+			   exclusive_bit(bit) + 1, state_name(bit)))
+		return 0;
+
 	return 1;
 }
 
-- 
2.14.1

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#1727223 — [RFC tip/locking v2 12/13] lockdep/selftest: Unleash irq_read_recursion2 and add more

Now since we can handle recursive read related irq inversion deadlocks
correctly, uncomment the irq_read_recursion2 and add more testcases.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 lib/locking-selftest.c | 59 ++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 47 insertions(+), 12 deletions(-)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index 1f794bb441a9..cbdcec6a776e 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -1051,20 +1051,28 @@ GENERATE_PERMUTATIONS_3_EVENTS(irq_inversion_soft_wlock)
 #define E3()				\
 					\
 	IRQ_ENTER();			\
-	RL(A);				\
+	LOCK(A);			\
 	L(B);				\
 	U(B);				\
-	RU(A);				\
+	UNLOCK(A);			\
 	IRQ_EXIT();
 
 /*
- * Generate 12 testcases:
+ * Generate 24 testcases:
  */
 #include "locking-selftest-hardirq.h"
-GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion_hard)
+#include "locking-selftest-rlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion_hard_rlock)
+
+#include "locking-selftest-wlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion_hard_wlock)
 
 #include "locking-selftest-softirq.h"
-GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion_soft)
+#include "locking-selftest-rlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion_soft_rlock)
+
+#include "locking-selftest-wlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion_soft_wlock)
 
 #undef E1
 #undef E2
@@ -1078,8 +1086,8 @@ GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion_soft)
 					\
 	IRQ_DISABLE();			\
 	L(B);				\
-	WL(A);				\
-	WU(A);				\
+	LOCK(A);			\
+	UNLOCK(A);			\
 	U(B);				\
 	IRQ_ENABLE();
 
@@ -1096,13 +1104,21 @@ GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion_soft)
 	IRQ_EXIT();
 
 /*
- * Generate 12 testcases:
+ * Generate 24 testcases:
  */
 #include "locking-selftest-hardirq.h"
-// GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion2_hard)
+#include "locking-selftest-rlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion2_hard_rlock)
+
+#include "locking-selftest-wlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion2_hard_wlock)
 
 #include "locking-selftest-softirq.h"
-// GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion2_soft)
+#include "locking-selftest-rlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion2_soft_rlock)
+
+#include "locking-selftest-wlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion2_soft_wlock)
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define I_SPINLOCK(x)	lockdep_reset_lock(&lock_##x.dep_map)
@@ -1255,6 +1271,25 @@ static inline void print_testname(const char *testname)
 	dotest(name##_rlock_##nr, SUCCESS, LOCKTYPE_RWLOCK);	\
 	pr_cont("\n");
 
+#define DO_TESTCASE_2RW(desc, name, nr)				\
+	print_testname(desc"/"#nr);				\
+	pr_cont("      |");					\
+	dotest(name##_wlock_##nr, FAILURE, LOCKTYPE_RWLOCK);	\
+	dotest(name##_rlock_##nr, SUCCESS, LOCKTYPE_RWLOCK);	\
+	pr_cont("\n");
+
+#define DO_TESTCASE_2x2RW(desc, name, nr)			\
+	DO_TESTCASE_2RW("hard-"desc, name##_hard, nr)		\
+	DO_TESTCASE_2RW("soft-"desc, name##_soft, nr)		\
+
+#define DO_TESTCASE_6x2x2RW(desc, name)				\
+	DO_TESTCASE_2x2RW(desc, name, 123);			\
+	DO_TESTCASE_2x2RW(desc, name, 132);			\
+	DO_TESTCASE_2x2RW(desc, name, 213);			\
+	DO_TESTCASE_2x2RW(desc, name, 231);			\
+	DO_TESTCASE_2x2RW(desc, name, 312);			\
+	DO_TESTCASE_2x2RW(desc, name, 321);
+
 #define DO_TESTCASE_6(desc, name)				\
 	print_testname(desc);					\
 	dotest(name##_spin, FAILURE, LOCKTYPE_SPIN);		\
@@ -2111,8 +2146,8 @@ void locking_selftest(void)
 	DO_TESTCASE_6x6("safe-A + unsafe-B #2", irqsafe4);
 	DO_TESTCASE_6x6RW("irq lock-inversion", irq_inversion);
 
-	DO_TESTCASE_6x2("irq read-recursion", irq_read_recursion);
-//	DO_TESTCASE_6x2B("irq read-recursion #2", irq_read_recursion2);
+	DO_TESTCASE_6x2x2RW("irq read-recursion", irq_read_recursion);
+	DO_TESTCASE_6x2x2RW("irq read-recursion #2", irq_read_recursion2);
 
 	ww_tests();
 
-- 
2.14.1

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#1727225 — [RFC tip/locking v2 07/13] lockdep: Support deadlock detection for recursive read in check_noncircular()

Currently, lockdep only has limit support for deadlock detection for
recursive read locks.

The basic idea of the detection is:

Since we make __bfs() able to traverse only the strong dependency paths,
so we report a circular deadlock if we could find a circle of a strong
dependency path.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/locking/lockdep.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index d9959f25247a..8a09b1a02342 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1345,6 +1345,14 @@ static inline int hlock_equal(struct lock_list *entry, void *data)
 	       (hlock->read == 2 || !entry->is_rr);
 }
 
+static inline int hlock_conflict(struct lock_list *entry, void *data)
+{
+	struct held_lock *hlock = (struct held_lock *)data;
+
+	return hlock_class(hlock) == entry->class &&
+	       (hlock->read != 2 || !entry->is_rr);
+}
+
 static noinline int print_circular_bug(struct lock_list *this,
 				struct lock_list *target,
 				struct held_lock *check_src,
@@ -1459,18 +1467,18 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
 }
 
 /*
- * Prove that the dependency graph starting at <entry> can not
+ * Prove that the dependency graph starting at <root> can not
  * lead to <target>. Print an error and return BFS_RMATCH if it does.
  */
 static noinline enum bfs_result
-check_noncircular(struct lock_list *root, struct lock_class *target,
+check_noncircular(struct lock_list *root, struct held_lock *target,
 		  struct lock_list **target_entry)
 {
 	enum bfs_result result;
 
 	debug_atomic_inc(nr_cyclic_checks);
 
-	result = __bfs_forwards(root, target, class_equal, target_entry);
+	result = __bfs_forwards(root, target, hlock_conflict, target_entry);
 
 	return result;
 }
-- 
2.14.1

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#1727226 — [RFC tip/locking v2 13/13] lockdep/selftest: Add more recursive read related test cases

Add those four test cases:

1.
	CPU1		CPU2		CPU3
	=============	=============	=============
	write_lock(X);
			write_lock(Y);
					write_lock(Z);
	read_lock(Y);
			read_lock(Z);
					read_lock(X);

	deadlock.

2.
	CPU1		CPU2		CPU3
	=============	=============	=============
	write_lock(X);
			read_lock(Y);
					write_lock(Z);
	write_lock(Y);
			read_lock(Z);
					read_lock(X);

	deadlock.

3.
	CPU1		CPU2		CPU3
	=============	=============	=============
	write_lock(X);
			read_lock(Y);
					read_lock(Z);
	write_lock(Y);
			read_lock(Z);
					write_lock(X);

	not deadlock.

4.
	CPU1		CPU2		CPU3
	=============	=============	=============
	write_lock(X);
			read_lock(Y);
					write_lock(Z);
	read_lock(Y);
			read_lock(Z);
					write_lock(X);

	not deadlock.

Those self testcases are valuable for the development of supporting
recursive read related deadlock detection.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 lib/locking-selftest.c | 161 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 161 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index cbdcec6a776e..0fe16f06ed00 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -1032,6 +1032,133 @@ GENERATE_PERMUTATIONS_3_EVENTS(irq_inversion_soft_wlock)
 #undef E2
 #undef E3
 
+/*
+ * write-read / write-read / write-read deadlock even if read is recursive
+ */
+
+#define E1()				\
+					\
+	WL(X1);				\
+	RL(Y1);				\
+	RU(Y1);				\
+	WU(X1);
+
+#define E2()				\
+					\
+	WL(Y1);				\
+	RL(Z1);				\
+	RU(Z1);				\
+	WU(Y1);
+
+#define E3()				\
+					\
+	WL(Z1);				\
+	RL(X1);				\
+	RU(X1);				\
+	WU(Z1);
+
+#include "locking-selftest-rlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(W1R2_W2R3_W3R1)
+
+#undef E1
+#undef E2
+#undef E3
+
+/*
+ * write-write / read-read / write-read deadlock even if read is recursive
+ */
+
+#define E1()				\
+					\
+	WL(X1);				\
+	WL(Y1);				\
+	WU(Y1);				\
+	WU(X1);
+
+#define E2()				\
+					\
+	RL(Y1);				\
+	RL(Z1);				\
+	RU(Z1);				\
+	RU(Y1);
+
+#define E3()				\
+					\
+	WL(Z1);				\
+	RL(X1);				\
+	RU(X1);				\
+	WU(Z1);
+
+#include "locking-selftest-rlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(W1W2_R2R3_W3R1)
+
+#undef E1
+#undef E2
+#undef E3
+
+/*
+ * write-write / read-read / read-write is not deadlock when read is recursive
+ */
+
+#define E1()				\
+					\
+	WL(X1);				\
+	WL(Y1);				\
+	WU(Y1);				\
+	WU(X1);
+
+#define E2()				\
+					\
+	RL(Y1);				\
+	RL(Z1);				\
+	RU(Z1);				\
+	RU(Y1);
+
+#define E3()				\
+					\
+	RL(Z1);				\
+	WL(X1);				\
+	WU(X1);				\
+	RU(Z1);
+
+#include "locking-selftest-rlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(W1R2_R2R3_W3W1)
+
+#undef E1
+#undef E2
+#undef E3
+
+/*
+ * write-read / read-read / write-write is not deadlock when read is recursive
+ */
+
+#define E1()				\
+					\
+	WL(X1);				\
+	RL(Y1);				\
+	RU(Y1);				\
+	WU(X1);
+
+#define E2()				\
+					\
+	RL(Y1);				\
+	RL(Z1);				\
+	RU(Z1);				\
+	RU(Y1);
+
+#define E3()				\
+					\
+	WL(Z1);				\
+	WL(X1);				\
+	WU(X1);				\
+	WU(Z1);
+
+#include "locking-selftest-rlock.h"
+GENERATE_PERMUTATIONS_3_EVENTS(W1W2_R2R3_R3W1)
+
+#undef E1
+#undef E2
+#undef E3
 /*
  * read-lock / write-lock recursion that is actually safe.
  */
@@ -1257,6 +1384,19 @@ static inline void print_testname(const char *testname)
 	dotest(name##_##nr, FAILURE, LOCKTYPE_RWLOCK);		\
 	pr_cont("\n");
 
+#define DO_TESTCASE_1RR(desc, name, nr)				\
+	print_testname(desc"/"#nr);				\
+	pr_cont("             |");				\
+	dotest(name##_##nr, SUCCESS, LOCKTYPE_RWLOCK);		\
+	pr_cont("\n");
+
+#define DO_TESTCASE_1RRB(desc, name, nr)			\
+	print_testname(desc"/"#nr);				\
+	pr_cont("             |");				\
+	dotest(name##_##nr, FAILURE, LOCKTYPE_RWLOCK);		\
+	pr_cont("\n");
+
+
 #define DO_TESTCASE_3(desc, name, nr)				\
 	print_testname(desc"/"#nr);				\
 	dotest(name##_spin_##nr, FAILURE, LOCKTYPE_SPIN);	\
@@ -1366,6 +1506,22 @@ static inline void print_testname(const char *testname)
 	DO_TESTCASE_2IB(desc, name, 312);			\
 	DO_TESTCASE_2IB(desc, name, 321);
 
+#define DO_TESTCASE_6x1RR(desc, name)				\
+	DO_TESTCASE_1RR(desc, name, 123);			\
+	DO_TESTCASE_1RR(desc, name, 132);			\
+	DO_TESTCASE_1RR(desc, name, 213);			\
+	DO_TESTCASE_1RR(desc, name, 231);			\
+	DO_TESTCASE_1RR(desc, name, 312);			\
+	DO_TESTCASE_1RR(desc, name, 321);
+
+#define DO_TESTCASE_6x1RRB(desc, name)				\
+	DO_TESTCASE_1RRB(desc, name, 123);			\
+	DO_TESTCASE_1RRB(desc, name, 132);			\
+	DO_TESTCASE_1RRB(desc, name, 213);			\
+	DO_TESTCASE_1RRB(desc, name, 231);			\
+	DO_TESTCASE_1RRB(desc, name, 312);			\
+	DO_TESTCASE_1RRB(desc, name, 321);
+
 #define DO_TESTCASE_6x6(desc, name)				\
 	DO_TESTCASE_6I(desc, name, 123);			\
 	DO_TESTCASE_6I(desc, name, 132);			\
@@ -2134,6 +2290,11 @@ void locking_selftest(void)
 	pr_cont("             |");
 	dotest(rlock_chaincache_ABBA1, FAILURE, LOCKTYPE_RWLOCK);
 
+	DO_TESTCASE_6x1RRB("rlock W1R2/W2R3/W3R1", W1R2_W2R3_W3R1);
+	DO_TESTCASE_6x1RRB("rlock W1W2/R2R3/W3R1", W1W2_R2R3_W3R1);
+	DO_TESTCASE_6x1RR("rlock W1W2/R2R3/R3W1", W1W2_R2R3_R3W1);
+	DO_TESTCASE_6x1RR("rlock W1R2/R2R3/W3W1", W1R2_R2R3_W3W1);
+
 	printk("  --------------------------------------------------------------------------\n");
 
 	/*
-- 
2.14.1

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#1727227 — [RFC tip/locking v2 03/13] lockdep: Change the meanings of LOCK_{USED_IN, ENABLED}_*_{READ}

We have three types of lock acquisitions: write, non-recursive read and
recursive read, and write and non-recursive read have no difference from
a viewpoint for deadlock detections, because a write acquisition of the
corresponding lock on an independent CPU or task makes a non-recursive
lock a write lock. So we could treat them as same types in lockdep(for
example, we can call them as non-recursive locks).

As to the irq lock inversion detection(safe->unsafe deadlock detection),
we used to differ write lock with read lock(non-recursive and
recursive), such a classification could be improved as non-recursive
read lock behaves the same as write lock, so this patch changes the
meanings of LOCK_{USED_IN, ENABLED}_*_{READ}.

old:
	LOCK_* : stands for write lock
	LOCK_*_READ: stands for read lock(non-recursive and recursive)
new:
	LOCK_* : stands for non-recursive(write lock and non-recursive
	read lock)
	LOCK_*_READ: stands for recursive read lock

(The names of them should be changed too to avoid confusion, so are the
related printks, however, this patch is simply for an RFC purpose
without too many unrelated changes, in the future, I could either add
necessary changes in next versions or leave those as TODOs)

Such a change is needed for a future improvement on recursive read
related irq inversion deadlock detection.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/locking/lockdep.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 5dbedcc571fd..86ef7ea9f79f 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3091,7 +3091,7 @@ static int mark_irqflags(struct task_struct *curr, struct held_lock *hlock)
 	 * mark the lock as used in these contexts:
 	 */
 	if (!hlock->trylock) {
-		if (hlock->read) {
+		if (hlock->read == 2) {
 			if (curr->hardirq_context)
 				if (!mark_lock(curr, hlock,
 						LOCK_USED_IN_HARDIRQ_READ))
@@ -3110,7 +3110,7 @@ static int mark_irqflags(struct task_struct *curr, struct held_lock *hlock)
 		}
 	}
 	if (!hlock->hardirqs_off) {
-		if (hlock->read) {
+		if (hlock->read == 2) {
 			if (!mark_lock(curr, hlock,
 					LOCK_ENABLED_HARDIRQ_READ))
 				return 0;
-- 
2.14.1

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#1727228 — [RFC tip/locking v2 04/13] lockdep: Introduce lock_list::dep

To add recursive read locks into the dependency graph, we need to store
the types of dependencies for the BFS later. There are four kinds of
dependencies:

*	Non-recursive -> Non-recursive dependencies(NN)
	e.g. write_lock(prev) -> write_lock(next)

*	Recursive -> Non-recursive dependencies(RN)
	e.g. read_lock(prev) -> write_lock(next);

*	Non-recursive -> recursive dependencies(NR)
	e.g. write_lock(prev) -> read_lock(next);

*	Recursive -> recursive dependencies(RR)
	e.g. read_lock(prev) -> read_lock(next);

Given a pair of two locks, four kinds of dependencies could all exist
between them, so we use 4 bit for the presence of each kind(stored in
lock_list::dep).

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 include/linux/lockdep.h  |  2 ++
 kernel/locking/lockdep.c | 46 ++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index bfa8e0b0d6f1..35b3fc0d6793 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -192,6 +192,8 @@ struct lock_list {
 	struct lock_class		*class;
 	struct stack_trace		trace;
 	int				distance;
+	/* bitmap of different dependencies from head to this */
+	u16				dep;
 
 	/*
 	 * The parent field is used to implement breadth-first search, and the
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 86ef7ea9f79f..1220dab7a506 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -884,6 +884,7 @@ static int add_lock_to_list(struct lock_class *this, struct list_head *head,
 		return 0;
 
 	entry->class = this;
+	entry->dep = dep;
 	entry->distance = distance;
 	entry->trace = *trace;
 	/*
@@ -1024,6 +1025,33 @@ static inline bool bfs_error(enum bfs_result res)
 	return res < 0;
 }
 
+#define DEP_NN_BIT 0
+#define DEP_RN_BIT 1
+#define DEP_NR_BIT 2
+#define DEP_RR_BIT 3
+
+#define DEP_NN_MASK (1U << (DEP_NN_BIT))
+#define DEP_RN_MASK (1U << (DEP_RN_BIT))
+#define DEP_NR_MASK (1U << (DEP_NR_BIT))
+#define DEP_RR_MASK (1U << (DEP_RR_BIT))
+
+static inline unsigned int __calc_dep_bit(int prev, int next)
+{
+	if (prev == 2 && next != 2)
+		return DEP_RN_BIT;
+	if (prev != 2 && next == 2)
+		return DEP_NR_BIT;
+	if (prev == 2 && next == 2)
+		return DEP_RR_BIT;
+	else
+		return DEP_NN_BIT;
+}
+
+static inline unsigned int calc_dep(int prev, int next)
+{
+	return 1U << __calc_dep_bit(prev, next);
+}
+
 static enum bfs_result __bfs(struct lock_list *source_entry,
 			     void *data,
 			     int (*match)(struct lock_list *entry, void *data),
@@ -1951,6 +1979,16 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 		if (entry->class == hlock_class(next)) {
 			if (distance == 1)
 				entry->distance = 1;
+			entry->dep |= calc_dep(prev->read, next->read);
+		}
+	}
+
+	/* Also, update the reverse dependency in @next's ->locks_before list */
+	list_for_each_entry(entry, &hlock_class(next)->locks_before, entry) {
+		if (entry->class == hlock_class(prev)) {
+			if (distance == 1)
+				entry->distance = 1;
+			entry->dep |= calc_dep(next->read, prev->read);
 			return 1;
 		}
 	}
@@ -1978,14 +2016,18 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	 */
 	ret = add_lock_to_list(hlock_class(next),
 			       &hlock_class(prev)->locks_after,
-			       next->acquire_ip, distance, trace);
+			       next->acquire_ip, distance,
+			       calc_dep(prev->read, next->read),
+			       trace);
 
 	if (!ret)
 		return 0;
 
 	ret = add_lock_to_list(hlock_class(prev),
 			       &hlock_class(next)->locks_before,
-			       next->acquire_ip, distance, trace);
+			       next->acquire_ip, distance,
+			       calc_dep(next->read, prev->read),
+			       trace);
 	if (!ret)
 		return 0;
 
-- 
2.14.1

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#1727230 — [RFC tip/locking v2 05/13] lockdep: Extend __bfs() to work with multiple kinds of dependencies

Now we have four kinds of dependencies in the dependency graph, and not
all the pathes carry strong dependencies, for example:

	Given lock A, B, C, if we have:

	CPU1			CPU2
	=============		==============
	write_lock(A);		read_lock(B);
	read_lock(B);		write_lock(C);

	then we have dependencies A--(NR)-->B, and B-->(RN)-->C, (NR and
	RN to indicate the dependency kind), A actually doesn't have
	strong dependency to C(IOW, C doesn't depend on A), to see this,
	let's say we have a third CPU3 doing:

	CPU3:
	=============
	write_lock(C);
	write_lock(A);

	, this is not a deadlock. However if we change the read_lock()
	on CPU2 to a write_lock(), it's a deadlock then.

	So A-->(NR)-->B-->(RN)-->C is not a strong dependency but
	A-->(NR)--B-->(NN)-->C is a strong dependency.

We can generalize this as: If a path of dependencies doesn't have two
adjacent dependencies as (*R)--L-->(R*), where L is some lock, it is a
strong dependency path, otherwise it's not.

Now our mission is to make __bfs() traverse only the strong dependency
paths, which is simple: we record whether we have --(*R)--> at the
current tail of the path in lock_list::is_rr, and whenever we pick a
dependency in the traverse, we 1) make sure we don't pick a --(R*)-->
dependency if our current tail is --(*R)--> and 2) greedily pick a
--(*N)--> as hard as possible.

With this extension for __bfs(), we now only need to initialize the root
of __bfs() properly(with a correct ->is_rr), to do so, we introduce some
helper functions, which also cleans up a little bit for the __bfs() root
initialization code.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 include/linux/lockdep.h  |  2 ++
 kernel/locking/lockdep.c | 85 +++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 68 insertions(+), 19 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 35b3fc0d6793..68cbe7e8399a 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -194,6 +194,8 @@ struct lock_list {
 	int				distance;
 	/* bitmap of different dependencies from head to this */
 	u16				dep;
+	/* used by BFS to record whether this is picked as a recursive read */
+	u16				is_rr;
 
 	/*
 	 * The parent field is used to implement breadth-first search, and the
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 1220dab7a506..3c43af353ea0 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -871,7 +871,7 @@ static struct lock_list *alloc_list_entry(void)
  * Add a new dependency to the head of the list:
  */
 static int add_lock_to_list(struct lock_class *this, struct list_head *head,
-			    unsigned long ip, int distance,
+			    unsigned long ip, int distance, unsigned int dep,
 			    struct stack_trace *trace)
 {
 	struct lock_list *entry;
@@ -1052,6 +1052,54 @@ static inline unsigned int calc_dep(int prev, int next)
 	return 1U << __calc_dep_bit(prev, next);
 }
 
+/*
+ * return -1 if no proper dependency could be picked
+ * return 0 if a * --> N dependency could be picked
+ * return 1 if only a * --> R dependency could be picked
+ *
+ * N: non-recursive lock
+ * R: recursive read lock
+ */
+static inline int pick_dep(u16 is_rr, u16 cap_dep)
+{
+	if (is_rr) { /* could only pick N --> */
+		if (cap_dep & DEP_NN_MASK)
+			return 0;
+		else if (cap_dep & DEP_NR_MASK)
+			return 1;
+		else
+			return -1;
+	} else {
+		if (cap_dep & DEP_NN_MASK || cap_dep & DEP_RN_MASK)
+			return 0;
+		else
+			return 1;
+	}
+}
+
+/*
+ * Initialize a lock_list entry @lock belonging to @class as the root for a BFS
+ * search.
+ */
+static inline void __bfs_init_root(struct lock_list *lock,
+				   struct lock_class *class)
+{
+	lock->class = class;
+	lock->parent = NULL;
+	lock->is_rr = 0;
+}
+
+/*
+ * Initialize a lock_list entry @lock based on a lock acquisition @hlock as the
+ * root for a BFS search.
+ */
+static inline void bfs_init_root(struct lock_list *lock,
+				 struct held_lock *hlock)
+{
+	__bfs_init_root(lock, hlock_class(hlock));
+	lock->is_rr = (hlock->read == 2);
+}
+
 static enum bfs_result __bfs(struct lock_list *source_entry,
 			     void *data,
 			     int (*match)(struct lock_list *entry, void *data),
@@ -1062,6 +1110,7 @@ static enum bfs_result __bfs(struct lock_list *source_entry,
 	struct list_head *head;
 	struct circular_queue *cq = &lock_cq;
 	enum bfs_result ret = BFS_RNOMATCH;
+	int is_rr, next_is_rr;
 
 	if (match(source_entry, data)) {
 		*target_entry = source_entry;
@@ -1107,11 +1156,18 @@ static enum bfs_result __bfs(struct lock_list *source_entry,
 		else
 			head = &lock->class->locks_before;
 
+		is_rr = lock->is_rr;
+
 		DEBUG_LOCKS_WARN_ON(!irqs_disabled());
 
 		list_for_each_entry_rcu(entry, head, entry) {
 			unsigned int cq_depth;
 
+			next_is_rr = pick_dep(is_rr, entry->dep);
+			if (next_is_rr < 0)
+				continue;
+			entry->is_rr = next_is_rr;
+
 			visit_lock_entry(entry, lock);
 			if (match(entry, data)) {
 				*target_entry = entry;
@@ -1362,8 +1418,7 @@ unsigned long lockdep_count_forward_deps(struct lock_class *class)
 	unsigned long ret, flags;
 	struct lock_list this;
 
-	this.parent = NULL;
-	this.class = class;
+	__bfs_init_root(&this, class);
 
 	local_irq_save(flags);
 	arch_spin_lock(&lockdep_lock);
@@ -1389,8 +1444,7 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
 	unsigned long ret, flags;
 	struct lock_list this;
 
-	this.parent = NULL;
-	this.class = class;
+	__bfs_init_root(&this, class);
 
 	local_irq_save(flags);
 	arch_spin_lock(&lockdep_lock);
@@ -1677,17 +1731,14 @@ check_usage(struct task_struct *curr, struct held_lock *prev,
 	struct lock_list *uninitialized_var(target_entry);
 	struct lock_list *uninitialized_var(target_entry1);
 
-	this.parent = NULL;
-
-	this.class = hlock_class(prev);
+	bfs_init_root(&this, prev);
 	ret = find_usage_backwards(&this, bit_backwards, &target_entry);
 	if (bfs_error(ret))
 		return print_bfs_bug(ret);
 	if (ret == BFS_RNOMATCH)
 		return 1;
 
-	that.parent = NULL;
-	that.class = hlock_class(next);
+	bfs_init_root(&that, next);
 	ret = find_usage_forwards(&that, bit_forwards, &target_entry1);
 	if (bfs_error(ret))
 		return print_bfs_bug(ret);
@@ -1946,9 +1997,8 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	 * We are using global variables to control the recursion, to
 	 * keep the stackframe size of the recursive functions low:
 	 */
-	this.class = hlock_class(next);
-	this.parent = NULL;
-	ret = check_noncircular(&this, hlock_class(prev), &target_entry);
+	bfs_init_root(&this, next);
+	ret = check_noncircular(&this, prev, &target_entry);
 	if (unlikely(ret == BFS_RMATCH))
 		return print_circular_bug(&this, target_entry, next, prev, trace);
 	else if (unlikely(bfs_error(ret)))
@@ -1996,8 +2046,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	/*
 	 * Is the <prev> -> <next> link redundant?
 	 */
-	this.class = hlock_class(prev);
-	this.parent = NULL;
+	bfs_init_root(&this, prev);
 	ret = check_redundant(&this, hlock_class(next), &target_entry);
 	if (ret == BFS_RMATCH) {
 		debug_atomic_inc(nr_redundant);
@@ -2762,8 +2811,7 @@ check_usage_forwards(struct task_struct *curr, struct held_lock *this,
 	struct lock_list root;
 	struct lock_list *uninitialized_var(target_entry);
 
-	root.parent = NULL;
-	root.class = hlock_class(this);
+	bfs_init_root(&root, this);
 	ret = find_usage_forwards(&root, bit, &target_entry);
 	if (bfs_error(ret))
 		return print_bfs_bug(ret);
@@ -2786,8 +2834,7 @@ check_usage_backwards(struct task_struct *curr, struct held_lock *this,
 	struct lock_list root;
 	struct lock_list *uninitialized_var(target_entry);
 
-	root.parent = NULL;
-	root.class = hlock_class(this);
+	bfs_init_root(&root, this);
 	ret = find_usage_backwards(&root, bit, &target_entry);
 	if (bfs_error(ret))
 		return print_bfs_bug(ret);
-- 
2.14.1

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#1727231 — [RFC tip/locking v2 09/13] lockdep: Add recursive read locks into dependency graph

Since we have all the fundamental to handle recursive read locks, we now
add them into the dependency graph.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/locking/lockdep.c | 16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 6659b91b70f2..b4f72a3380c3 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2033,16 +2033,6 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	if (!check_prev_add_irq(curr, prev, next))
 		return 0;
 
-	/*
-	 * For recursive read-locks we do all the dependency checks,
-	 * but we dont store read-triggered dependencies (only
-	 * write-triggered dependencies). This ensures that only the
-	 * write-side dependencies matter, and that if for example a
-	 * write-lock never takes any other locks, then the reads are
-	 * equivalent to a NOP.
-	 */
-	if (next->read == 2 || prev->read == 2)
-		return 1;
 	/*
 	 * Is the <prev> -> <next> dependency already present?
 	 *
@@ -2164,7 +2154,7 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
 			 * Only non-recursive-read entries get new dependencies
 			 * added:
 			 */
-			if (hlock->read != 2 && hlock->check) {
+			if (hlock->check) {
 				int ret = check_prev_add(curr, hlock, next,
 							 distance, &trace, save);
 				if (!ret)
@@ -4965,7 +4955,7 @@ static inline struct lock_class *xlock_class(struct cross_lock *xlock)
  */
 static inline int depend_before(struct held_lock *hlock)
 {
-	return hlock->read != 2 && hlock->check && !hlock->trylock;
+	return hlock->check && !hlock->trylock;
 }
 
 /*
@@ -4973,7 +4963,7 @@ static inline int depend_before(struct held_lock *hlock)
  */
 static inline int depend_after(struct held_lock *hlock)
 {
-	return hlock->read != 2 && hlock->check;
+	return hlock->check;
 }
 
 /*
-- 
2.14.1

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#1727232 — [RFC tip/locking v2 11/13] lockdep: Take read/write status in consideration when generate chainkey

Currently, the chainkey of a lock chain is a hash sum of the class_idx
of all the held locks, the read/write status are not taken in to
consideration while generating the chainkey. This could result into a
problem, if we have:

	P1()
	{
		read_lock(B);
		lock(A);
	}

	P2()
	{
		lock(A);
		read_lock(B);
	}

	P3()
	{
		lock(A);
		write_lock(B);
	}

, and P1(), P2(), P3() run one by one, when running P2(), it's detected
such a lock chain A -> B is not a deadlock, then it's added in the chain
cache, and then when running P3(), even if it's a deadlock, we could
miss it because of the hit of chain cache. This could be confirmed by
self testcase "chain cached mixed R-L/L-W ".

To resolve this, we use "hlock_id" to generate the chainkey, the
hlock_id is a tuple (hlock->class_idx, hlock->read), which fits in a u16
type. With this, the chainkeys are different is the lock sequences have
the same locks but different read/write status.

Besides, since we use "hlock_id" to generate chainkeys, the chain_hlocks
now store the "hlock_id"s rather than lock_class indexes.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/locking/lockdep.c | 60 ++++++++++++++++++++++++++++++------------------
 1 file changed, 38 insertions(+), 22 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index b4f72a3380c3..9f7a02315c6a 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -311,6 +311,21 @@ static struct hlist_head classhash_table[CLASSHASH_SIZE];
 
 static struct hlist_head chainhash_table[CHAINHASH_SIZE];
 
+/*
+ * the id  chain_hlocks
+ */
+static inline u16 hlock_id(struct held_lock *hlock)
+{
+	BUILD_BUG_ON(MAX_LOCKDEP_KEYS_BITS + 2 > 16);
+
+	return (hlock->class_idx | (hlock->read << MAX_LOCKDEP_KEYS_BITS));
+}
+
+static inline unsigned int chain_hlock_class_idx(u16 hlock_id)
+{
+	return hlock_id & MAX_LOCKDEP_KEYS;
+}
+
 /*
  * The hash key of the lock dependency chains is a hash itself too:
  * it's a hash of all locks taken up to that lock, including that lock.
@@ -2212,7 +2227,10 @@ static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
 
 struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
 {
-	return lock_classes + chain_hlocks[chain->base + i];
+	u16 chain_hlock = chain_hlocks[chain->base + i];
+	unsigned int class_idx = chain_hlock_class_idx(chain_hlock);
+
+	return lock_classes + class_idx - 1;
 }
 
 /*
@@ -2238,12 +2256,12 @@ static inline int get_first_held_lock(struct task_struct *curr,
 /*
  * Returns the next chain_key iteration
  */
-static u64 print_chain_key_iteration(int class_idx, u64 chain_key)
+static u64 print_chain_key_iteration(u16 hlock_id, u64 chain_key)
 {
-	u64 new_chain_key = iterate_chain_key(chain_key, class_idx);
+	u64 new_chain_key = iterate_chain_key(chain_key, hlock_id);
 
-	printk(" class_idx:%d -> chain_key:%016Lx",
-		class_idx,
+	printk(" hlock_id:%d -> chain_key:%016Lx",
+		(unsigned int)hlock_id,
 		(unsigned long long)new_chain_key);
 	return new_chain_key;
 }
@@ -2259,12 +2277,12 @@ print_chain_keys_held_locks(struct task_struct *curr, struct held_lock *hlock_ne
 	printk("depth: %u\n", depth + 1);
 	for (i = get_first_held_lock(curr, hlock_next); i < depth; i++) {
 		hlock = curr->held_locks + i;
-		chain_key = print_chain_key_iteration(hlock->class_idx, chain_key);
+		chain_key = print_chain_key_iteration(hlock_id(hlock), chain_key);
 
 		print_lock(hlock);
 	}
 
-	print_chain_key_iteration(hlock_next->class_idx, chain_key);
+	print_chain_key_iteration(hlock_id(hlock_next), chain_key);
 	print_lock(hlock_next);
 }
 
@@ -2272,14 +2290,14 @@ static void print_chain_keys_chain(struct lock_chain *chain)
 {
 	int i;
 	u64 chain_key = 0;
-	int class_id;
+	u16 hlock_id;
 
 	printk("depth: %u\n", chain->depth);
 	for (i = 0; i < chain->depth; i++) {
-		class_id = chain_hlocks[chain->base + i];
-		chain_key = print_chain_key_iteration(class_id + 1, chain_key);
+		hlock_id = chain_hlocks[chain->base + i];
+		chain_key = print_chain_key_iteration(hlock_id, chain_key);
 
-		print_lock_name(lock_classes + class_id);
+		print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id) - 1);
 		printk("\n");
 	}
 }
@@ -2328,7 +2346,7 @@ static int check_no_collision(struct task_struct *curr,
 	}
 
 	for (j = 0; j < chain->depth - 1; j++, i++) {
-		id = curr->held_locks[i].class_idx - 1;
+		id = hlock_id(&curr->held_locks[i]);
 
 		if (DEBUG_LOCKS_WARN_ON(chain_hlocks[chain->base + j] != id)) {
 			print_collision(curr, hlock, chain);
@@ -2385,8 +2403,8 @@ static inline int add_chain_cache_classes(unsigned int prev,
 	if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
 		chain->base = nr_chain_hlocks;
 		nr_chain_hlocks += chain->depth;
-		chain_hlocks[chain->base] = prev - 1;
-		chain_hlocks[chain->base + 1] = next -1;
+		chain_hlocks[chain->base] = prev;
+		chain_hlocks[chain->base + 1] = next;
 	}
 #ifdef CONFIG_DEBUG_LOCKDEP
 	/*
@@ -2420,7 +2438,6 @@ static inline int add_chain_cache(struct task_struct *curr,
 				  struct held_lock *hlock,
 				  u64 chain_key)
 {
-	struct lock_class *class = hlock_class(hlock);
 	struct hlist_head *hash_head = chainhashentry(chain_key);
 	struct lock_chain *chain;
 	int i, j;
@@ -2459,10 +2476,9 @@ static inline int add_chain_cache(struct task_struct *curr,
 	if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
 		chain->base = nr_chain_hlocks;
 		for (j = 0; j < chain->depth - 1; j++, i++) {
-			int lock_id = curr->held_locks[i].class_idx - 1;
-			chain_hlocks[chain->base + j] = lock_id;
+			chain_hlocks[chain->base + j] = hlock_id(&curr->held_locks[i]);
 		}
-		chain_hlocks[chain->base + j] = class - lock_classes;
+		chain_hlocks[chain->base + j] = hlock_id(hlock);
 	}
 
 	if (nr_chain_hlocks < MAX_LOCKDEP_CHAIN_HLOCKS)
@@ -2660,7 +2676,7 @@ static void check_chain_key(struct task_struct *curr)
 		if (prev_hlock && (prev_hlock->irq_context !=
 							hlock->irq_context))
 			chain_key = 0;
-		chain_key = iterate_chain_key(chain_key, hlock->class_idx);
+		chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
 		prev_hlock = hlock;
 	}
 	if (chain_key != curr->curr_chain_key) {
@@ -3626,7 +3642,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 		chain_key = 0;
 		chain_head = 1;
 	}
-	chain_key = iterate_chain_key(chain_key, class_idx);
+	chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
 
 	if (nest_lock && !__lock_is_held(nest_lock, -1))
 		return print_lock_nested_lock_not_held(curr, hlock, ip);
@@ -5136,9 +5152,9 @@ 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;
+	xid = xlock_class(xlock) - lock_classes + 1;
 	chain_key = iterate_chain_key((u64)0, xid);
-	pid = xhlock_class(xhlock) - lock_classes;
+	pid = xhlock_class(xhlock) - lock_classes + 1;
 	chain_key = iterate_chain_key(chain_key, pid);
 
 	if (lookup_chain_cache(chain_key))
-- 
2.14.1

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#1727233 — [RFC tip/locking v2 02/13] lockdep: Make __bfs() visit every dependency rather than every class until a match

Currently, __bfs() will do a breadth-first search in the dependency
graph and visit each lock class in the graph exactly once, so for
example, in the following graph:

	A ---------> B
	|            ^
	|            |
	+----------> C

a __bfs() call starts at A, will visit B through dependency A -> B and
visit C through dependency C -> B and that's it.

This is OK for now, as we only have strong dependencies in the
dependency graph, so whenever there is a traverse path from A to B in
__bfs(), it means A has strong dependency to B(IOW, B depends on A). So
no need to visit all dependencies in the graph.

However, as we are going to add recursive-read lock into the dependency
graph, not all the paths mean strong dependencies afterwards, in the
same example above, dependency A --> B may be a weak dependency and
traverse A -> C -> B may be a strong dependency path. So now we need to
visit each dependency in the graph once in __bfs() until a match.

The solution is simple:

We used to mark lock_class::lockdep_dependency_gen_id to indicate a
class has been visited in __bfs(), now we change the semantics a little
bit, we now mark lock_class::lockdep_dependency_gen_id to indicate all
the dependencies in its lock_{after,before} have been visited in the
__bfs(), note we only take one direction in a __bfs() search. In this
way, each dependency is guaranteed to be visited until we find a match.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/locking/lockdep.c | 61 +++++++++++++++++++++++++++---------------------
 1 file changed, 34 insertions(+), 27 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index df0b7e620659..5dbedcc571fd 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -960,24 +960,20 @@ static inline unsigned int  __cq_get_elem_count(struct circular_queue *cq)
 	return (cq->rear - cq->front) & CQ_MASK;
 }
 
-static inline void mark_lock_accessed(struct lock_list *lock,
-					struct lock_list *parent)
+static inline void mark_lock_list_accessed(struct lock_class *class)
 {
-	unsigned long nr;
+	class->dep_gen_id = lockdep_dependency_gen_id;
+}
 
-	nr = lock - list_entries;
-	WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
+static inline void visit_lock_entry(struct lock_list *lock,
+				    struct lock_list *parent)
+{
 	lock->parent = parent;
-	lock->class->dep_gen_id = lockdep_dependency_gen_id;
 }
 
-static inline unsigned long lock_accessed(struct lock_list *lock)
+static inline unsigned long lock_list_accessed(struct lock_class *class)
 {
-	unsigned long nr;
-
-	nr = lock - list_entries;
-	WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
-	return lock->class->dep_gen_id == lockdep_dependency_gen_id;
+	return class->dep_gen_id == lockdep_dependency_gen_id;
 }
 
 static inline struct lock_list *get_lock_parent(struct lock_list *child)
@@ -1066,6 +1062,18 @@ static enum bfs_result __bfs(struct lock_list *source_entry,
 			goto exit;
 		}
 
+		/*
+		 * If we have visited all the dependencies from this @lock to
+		 * others(iow, if we have visited all lock_list entries in
+		 * @lock->class->locks_{after,before}, we skip, otherwise go
+		 * and visit all the dependencies in the list and mark this
+		 * list accessed.
+		 */
+		if (lock_list_accessed(lock->class))
+			continue;
+		else
+			mark_lock_list_accessed(lock->class);
+
 		if (forward)
 			head = &lock->class->locks_after;
 		else
@@ -1074,23 +1082,22 @@ static enum bfs_result __bfs(struct lock_list *source_entry,
 		DEBUG_LOCKS_WARN_ON(!irqs_disabled());
 
 		list_for_each_entry_rcu(entry, head, entry) {
-			if (!lock_accessed(entry)) {
-				unsigned int cq_depth;
-				mark_lock_accessed(entry, lock);
-				if (match(entry, data)) {
-					*target_entry = entry;
-					ret = BFS_RMATCH;
-					goto exit;
-				}
+			unsigned int cq_depth;
 
-				if (__cq_enqueue(cq, (unsigned long)entry)) {
-					ret = BFS_EQUEUEFULL;
-					goto exit;
-				}
-				cq_depth = __cq_get_elem_count(cq);
-				if (max_bfs_queue_depth < cq_depth)
-					max_bfs_queue_depth = cq_depth;
+			visit_lock_entry(entry, lock);
+			if (match(entry, data)) {
+				*target_entry = entry;
+				ret = BFS_RMATCH;
+				goto exit;
+			}
+
+			if (__cq_enqueue(cq, (unsigned long)entry)) {
+				ret = BFS_EQUEUEFULL;
+				goto exit;
 			}
+			cq_depth = __cq_get_elem_count(cq);
+			if (max_bfs_queue_depth < cq_depth)
+				max_bfs_queue_depth = cq_depth;
 		}
 	}
 exit:
-- 
2.14.1

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#1727234 — [RFC tip/locking v2 06/13] lockdep: Adjust check_redundant() for recursive read change

As we have four kinds of dependencies now, check_redundant() should only
report redundant if we have a dependency path which is equal or
_stronger_ than the current dependency. For example if check_prev_add()
we have:

	prev->read == 2 && next->read != 2

, we should only report redundant if we find a path like:

	prev--(RN)-->....--(*N)-->next

and if we have:

	prev->read == 2 && next->read == 2

, we could report redundant if we find a path like:

	prev--(RN)-->....--(*N)-->next

or

	prev--(RN)-->....--(*R)-->next

To do so, we need to pass the recursive-read status of next into
check_redundant(). This patch changes the parameter of check_redundant()
and the match function to achieve this.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/locking/lockdep.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 3c43af353ea0..d9959f25247a 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1337,9 +1337,12 @@ print_circular_bug_header(struct lock_list *entry, unsigned int depth,
 	return 0;
 }
 
-static inline int class_equal(struct lock_list *entry, void *data)
+static inline int hlock_equal(struct lock_list *entry, void *data)
 {
-	return entry->class == data;
+	struct held_lock *hlock = (struct held_lock *)data;
+
+	return hlock_class(hlock) == entry->class &&
+	       (hlock->read == 2 || !entry->is_rr);
 }
 
 static noinline int print_circular_bug(struct lock_list *this,
@@ -1473,14 +1476,14 @@ check_noncircular(struct lock_list *root, struct lock_class *target,
 }
 
 static noinline enum bfs_result
-check_redundant(struct lock_list *root, struct lock_class *target,
+check_redundant(struct lock_list *root, struct held_lock *target,
 		struct lock_list **target_entry)
 {
 	enum bfs_result result;
 
 	debug_atomic_inc(nr_redundant_checks);
 
-	result = __bfs_forwards(root, target, class_equal, target_entry);
+	result = __bfs_forwards(root, target, hlock_equal, target_entry);
 
 	return result;
 }
@@ -2047,7 +2050,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	 * Is the <prev> -> <next> link redundant?
 	 */
 	bfs_init_root(&this, prev);
-	ret = check_redundant(&this, hlock_class(next), &target_entry);
+	ret = check_redundant(&this, next, &target_entry);
 	if (ret == BFS_RMATCH) {
 		debug_atomic_inc(nr_redundant);
 		return 2;
-- 
2.14.1

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#1727236 — [RFC tip/locking v2 10/13] lockdep/selftest: Add a R-L/L-W test case specific to chain cache behavior

As our chain cache doesn't differ read/write locks, so even we can
detect a read-lock/lock-write deadlock in check_noncircular(), we can
still be fooled if a read-lock/lock-read case(which is not a deadlock)
comes first.

So introduce this test case to test specific to the chain cache behavior
on detecting recursive read lock related deadlocks.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 lib/locking-selftest.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index cd0b5c964bd0..1f794bb441a9 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -394,6 +394,49 @@ static void rwsem_ABBA1(void)
 	MU(Y1); // should fail
 }
 
+/*
+ * read_lock(A)
+ * spin_lock(B)
+ *		spin_lock(B)
+ *		write_lock(A)
+ *
+ * This test case is aimed at poking whether the chain cache prevents us from
+ * detecting a read-lock/lock-write deadlock: if the chain cache doesn't differ
+ * read/write locks, the following case may happen
+ *
+ * 	{ read_lock(A)->lock(B) dependency exists }
+ *
+ * 	P0:
+ * 	lock(B);
+ * 	read_lock(A);
+ *
+ *	{ Not a deadlock, B -> A is added in the chain cache }
+ *
+ *	P1:
+ *	lock(B);
+ *	write_lock(A);
+ *
+ *	{ B->A found in chain cache, not reported as a deadlock }
+ *
+ */
+static void rlock_chaincache_ABBA1(void)
+{
+	RL(X1);
+	L(Y1);
+	U(Y1);
+	RU(X1);
+
+	L(Y1);
+	RL(X1);
+	RU(X1);
+	U(Y1);
+
+	L(Y1);
+	WL(X1);
+	WU(X1);
+	U(Y1); // should fail
+}
+
 /*
  * read_lock(A)
  * spin_lock(B)
@@ -2052,6 +2095,10 @@ void locking_selftest(void)
 	pr_cont("             |");
 	dotest(rwsem_ABBA3, FAILURE, LOCKTYPE_RWSEM);
 
+	print_testname("chain cached mixed R-L/L-W ABBA");
+	pr_cont("             |");
+	dotest(rlock_chaincache_ABBA1, FAILURE, LOCKTYPE_RWLOCK);
+
 	printk("  --------------------------------------------------------------------------\n");
 
 	/*
-- 
2.14.1

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#1727240 — Re: [RFC tip/locking v2 00/13] lockdep: Support deadlock detection for recursive read locks

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On Wed, Sep 06, 2017 at 04:28:11PM +0800, Boqun Feng wrote:
> Hi Ingo and Peter,
> 
> This is V2 for recursive read lock support in lockdep. I fix several
> bugs in V1 and also add irq inversion detection support for recursive
> read locks.
> 
> V1: https://marc.info/?l=linux-kernel&m=150393341825453
> 
> 
> As Peter pointed out:
> 
> 	https://marc.info/?l=linux-kernel&m=150349072023540
> 
> The lockdep current has a limit support for recursive read locks, the
> deadlock case as follow could not be detected:
> 
> 	read_lock(A);
> 				lock(B);
> 	lock(B);
> 				write_lock(A);
> 
> I got some inspiration from Gautham R Shenoy:
> 
> 	https://lwn.net/Articles/332801/
> 
> , and came up with this series.
> 
> The basic idea is:
> 
> *	Add recursive read locks into the graph
> 
> *	Classify dependencies into --(RR)-->, --(NR)-->, --(RN)-->,
> 	--(NN)-->, where R stands for recursive read lock, N stands for
> 	other locks(i.e. non-recursive read locks and write locks).
> 
> *	Define strong dependency paths as the paths of dependencies
> 	don't have two adjacent dependencies as --(*R)--> and --(R*)-->.
> 
> *	Extend __bfs() to only traverse on strong dependency paths.
> 
> *	If __bfs() finds a strong dependency circle, then a deadlock is
> 	reported.
> 
> The whole series is based on current master branch of Linus' tree:
> 
> 	e7d0c41ecc2e ("Merge tag 'devprop-4.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm")
> 
> , and I also put it at:
> 
> 	git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git arr-rfc-v2

Hmm.. should revert

	d82fed752942 ("locking/lockdep/selftests: Fix mixed read-write ABBA tests")

for testing, as it is a work around because of we had limit support for
recursive read lock before.

I put a branch with that reverted at:

 	git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git arr-rfc-v2a

Selftest passed for that branch, now run it for more time.

Regards,
Boqun

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