[GIT PULL] [PATCH 0/3] LOCKDEP changes for v6.16

[GIT PULL] [PATCH 0/3] LOCKDEP changes for v6.16

[Boqun Feng]

Hi Ingo & Peter,

Please pull the lockdep changes for v6.16 into tip. I'm sending the
changes in patchset, but I also created a tag and the pull-request
message in case you want to directly pull. Thanks!

Regards,
Boqun

The following changes since commit 35e6b537af85d97e0aafd8f2829dfa884a22df20:

  lockdep: Remove disable_irq_lockdep() (2025-03-14 21:13:20 +0100)

are available in the Git repository at:

  git@gitolite.kernel.org:pub/scm/linux/kernel/git/boqun/linux tags/lockdep-for-tip.2025.05.05

for you to fetch changes up to b3eec4e26ada8a71c40147b45026d2345f3b6ae3:

  locking/lockdep: Add # of dynamic keys stat to /proc/lockdep_stats (2025-05-04 11:03:02 -0700)

----------------------------------------------------------------
Lockdep changes for v6.16:

- Move hlock_equal() only under CONFIG_LOCKDEP_SMALL=y
- Prevent abuse of lockdep subclass in __lock_acquire()
- Add # of dynamic keys stat to /proc/lockdep_stats

----------------------------------------------------------------
Andy Shevchenko (1):
      lockdep: Move hlock_equal() to the respective ifdeffery

Waiman Long (2):
      locking/lockdep: Prevent abuse of lockdep subclass
      locking/lockdep: Add # of dynamic keys stat to /proc/lockdep_stats

 kernel/locking/lockdep.c           | 76 ++++++++++++++++++++------------------
 kernel/locking/lockdep_internals.h |  1 +
 kernel/locking/lockdep_proc.c      |  2 +
 3 files changed, 44 insertions(+), 35 deletions(-)

-- 
2.39.5 (Apple Git-154)

[PATCH 1/3] lockdep: Move hlock_equal() to the respective ifdeffery

[Boqun Feng]

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

When hlock_equal() is unused, it prevents kernel builds with clang,
`make W=1` and CONFIG_WERROR=y, CONFIG_LOCKDEP=y and
CONFIG_LOCKDEP_SMALL=n:

  lockdep.c:2005:20: error: unused function 'hlock_equal' [-Werror,-Wunused-function]

Fix this by moving the function to the respective existing ifdeffery
for its the only user.

See also commit 6863f5643dd7 ("kbuild: allow Clang to find unused static
inline functions for W=1 build").

Fixes: 68e305678583 ("lockdep: Adjust check_redundant() for recursive read change")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250415085857.495543-1-andriy.shevchenko@linux.intel.com
---
 kernel/locking/lockdep.c | 70 ++++++++++++++++++++--------------------
 1 file changed, 35 insertions(+), 35 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index b15757e63626..ff2ce90a87bc 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1976,41 +1976,6 @@ print_circular_bug_header(struct lock_list *entry, unsigned int depth,
 	print_circular_bug_entry(entry, depth);
 }
 
-/*
- * We are about to add A -> B into the dependency graph, and in __bfs() a
- * strong dependency path A -> .. -> B is found: hlock_class equals
- * entry->class.
- *
- * If A -> .. -> B can replace A -> B in any __bfs() search (means the former
- * is _stronger_ than or equal to the latter), we consider A -> B as redundant.
- * For example if A -> .. -> B is -(EN)-> (i.e. A -(E*)-> .. -(*N)-> B), and A
- * -> B is -(ER)-> or -(EN)->, then we don't need to add A -> B into the
- * dependency graph, as any strong path ..-> A -> B ->.. we can get with
- * having dependency A -> B, we could already get a equivalent path ..-> A ->
- * .. -> B -> .. with A -> .. -> B. Therefore A -> B is redundant.
- *
- * We need to make sure both the start and the end of A -> .. -> B is not
- * weaker than A -> B. For the start part, please see the comment in
- * check_redundant(). For the end part, we need:
- *
- * Either
- *
- *     a) A -> B is -(*R)-> (everything is not weaker than that)
- *
- * or
- *
- *     b) A -> .. -> B is -(*N)-> (nothing is stronger than this)
- *
- */
-static inline bool hlock_equal(struct lock_list *entry, void *data)
-{
-	struct held_lock *hlock = (struct held_lock *)data;
-
-	return hlock_class(hlock) == entry->class && /* Found A -> .. -> B */
-	       (hlock->read == 2 ||  /* A -> B is -(*R)-> */
-		!entry->only_xr); /* A -> .. -> B is -(*N)-> */
-}
-
 /*
  * We are about to add B -> A into the dependency graph, and in __bfs() a
  * strong dependency path A -> .. -> B is found: hlock_class equals
@@ -2915,6 +2880,41 @@ static inline bool usage_skip(struct lock_list *entry, void *mask)
 #endif /* CONFIG_TRACE_IRQFLAGS */
 
 #ifdef CONFIG_LOCKDEP_SMALL
+/*
+ * We are about to add A -> B into the dependency graph, and in __bfs() a
+ * strong dependency path A -> .. -> B is found: hlock_class equals
+ * entry->class.
+ *
+ * If A -> .. -> B can replace A -> B in any __bfs() search (means the former
+ * is _stronger_ than or equal to the latter), we consider A -> B as redundant.
+ * For example if A -> .. -> B is -(EN)-> (i.e. A -(E*)-> .. -(*N)-> B), and A
+ * -> B is -(ER)-> or -(EN)->, then we don't need to add A -> B into the
+ * dependency graph, as any strong path ..-> A -> B ->.. we can get with
+ * having dependency A -> B, we could already get a equivalent path ..-> A ->
+ * .. -> B -> .. with A -> .. -> B. Therefore A -> B is redundant.
+ *
+ * We need to make sure both the start and the end of A -> .. -> B is not
+ * weaker than A -> B. For the start part, please see the comment in
+ * check_redundant(). For the end part, we need:
+ *
+ * Either
+ *
+ *     a) A -> B is -(*R)-> (everything is not weaker than that)
+ *
+ * or
+ *
+ *     b) A -> .. -> B is -(*N)-> (nothing is stronger than this)
+ *
+ */
+static inline bool hlock_equal(struct lock_list *entry, void *data)
+{
+	struct held_lock *hlock = (struct held_lock *)data;
+
+	return hlock_class(hlock) == entry->class && /* Found A -> .. -> B */
+	       (hlock->read == 2 ||  /* A -> B is -(*R)-> */
+		!entry->only_xr); /* A -> .. -> B is -(*N)-> */
+}
+
 /*
  * Check that the dependency graph starting at <src> can lead to
  * <target> or not. If it can, <src> -> <target> dependency is already
-- 
2.39.5 (Apple Git-154)

[PATCH 2/3] locking/lockdep: Prevent abuse of lockdep subclass

[Boqun Feng]

From: Waiman Long <longman@redhat.com>

To catch the code trying to use a subclass value >=
MAX_LOCKDEP_SUBCLASSES (8), add a DEBUG_LOCKS_WARN_ON() statement to
notify the users that such a large value is not allowed.

[boqun: Reword the commit log with a more objective tone]

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250409143751.2010391-1-longman@redhat.com
---
 kernel/locking/lockdep.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index ff2ce90a87bc..58883c8375d1 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5101,6 +5101,9 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 		lockevent_inc(lockdep_nocheck);
 	}
 
+	if (DEBUG_LOCKS_WARN_ON(subclass >= MAX_LOCKDEP_SUBCLASSES))
+		return 0;
+
 	if (subclass < NR_LOCKDEP_CACHING_CLASSES)
 		class = lock->class_cache[subclass];
 	/*
-- 
2.39.5 (Apple Git-154)

[PATCH 3/3] locking/lockdep: Add # of dynamic keys stat to /proc/lockdep_stats

[Boqun Feng]

From: Waiman Long <longman@redhat.com>

There have been recent reports about running out of lockdep keys
(MAX_LOCKDEP_KEYS too low!). One possible reason is that too many
dynamic keys have been registered. A possible culprit is the
lockdep_register_key() call in qdisc_alloc() of net/sched/sch_generic.c.

Currently, there is no way to find out how many dynamic keys have been
registered. Add such a stat to the /proc/lockdep_stats to get better
clarity.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250425001155.775458-1-longman@redhat.com
---
 kernel/locking/lockdep.c           | 3 +++
 kernel/locking/lockdep_internals.h | 1 +
 kernel/locking/lockdep_proc.c      | 2 ++
 3 files changed, 6 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 58883c8375d1..e7166ff64681 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -219,6 +219,7 @@ static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES);
 static struct hlist_head lock_keys_hash[KEYHASH_SIZE];
 unsigned long nr_lock_classes;
 unsigned long nr_zapped_classes;
+unsigned long nr_dynamic_keys;
 unsigned long max_lock_class_idx;
 struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
 DECLARE_BITMAP(lock_classes_in_use, MAX_LOCKDEP_KEYS);
@@ -1238,6 +1239,7 @@ void lockdep_register_key(struct lock_class_key *key)
 			goto out_unlock;
 	}
 	hlist_add_head_rcu(&key->hash_entry, hash_head);
+	nr_dynamic_keys++;
 out_unlock:
 	graph_unlock();
 restore_irqs:
@@ -6606,6 +6608,7 @@ void lockdep_unregister_key(struct lock_class_key *key)
 		pf = get_pending_free();
 		__lockdep_free_key_range(pf, key, 1);
 		need_callback = prepare_call_rcu_zapped(pf);
+		nr_dynamic_keys--;
 	}
 	lockdep_unlock();
 	raw_local_irq_restore(flags);
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 20f9ef58d3d0..82156caf77d1 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -138,6 +138,7 @@ extern unsigned long nr_lock_classes;
 extern unsigned long nr_zapped_classes;
 extern unsigned long nr_zapped_lock_chains;
 extern unsigned long nr_list_entries;
+extern unsigned long nr_dynamic_keys;
 long lockdep_next_lockchain(long i);
 unsigned long lock_chain_count(void);
 extern unsigned long nr_stack_trace_entries;
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index 6db0f43fc4df..b52c07c4707c 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -286,6 +286,8 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
 #endif
 	seq_printf(m, " lock-classes:                  %11lu [max: %lu]\n",
 			nr_lock_classes, MAX_LOCKDEP_KEYS);
+	seq_printf(m, " dynamic-keys:                  %11lu\n",
+			nr_dynamic_keys);
 	seq_printf(m, " direct dependencies:           %11lu [max: %lu]\n",
 			nr_list_entries, MAX_LOCKDEP_ENTRIES);
 	seq_printf(m, " indirect dependencies:         %11lu\n",
-- 
2.39.5 (Apple Git-154)

Re: [GIT PULL] [PATCH 0/3] LOCKDEP changes for v6.16

[Ingo Molnar]

* Boqun Feng <boqun.feng@gmail.com> wrote:

> Hi Ingo & Peter,
> 
> Please pull the lockdep changes for v6.16 into tip. I'm sending the
> changes in patchset, but I also created a tag and the pull-request
> message in case you want to directly pull. Thanks!
> 
> Regards,
> Boqun
> 
> The following changes since commit 35e6b537af85d97e0aafd8f2829dfa884a22df20:
> 
>   lockdep: Remove disable_irq_lockdep() (2025-03-14 21:13:20 +0100)
> 
> are available in the Git repository at:
> 
>   git@gitolite.kernel.org:pub/scm/linux/kernel/git/boqun/linux tags/lockdep-for-tip.2025.05.05
> 
> for you to fetch changes up to b3eec4e26ada8a71c40147b45026d2345f3b6ae3:
> 
>   locking/lockdep: Add # of dynamic keys stat to /proc/lockdep_stats (2025-05-04 11:03:02 -0700)
> 
> ----------------------------------------------------------------
> Lockdep changes for v6.16:
> 
> - Move hlock_equal() only under CONFIG_LOCKDEP_SMALL=y
> - Prevent abuse of lockdep subclass in __lock_acquire()
> - Add # of dynamic keys stat to /proc/lockdep_stats
> 
> ----------------------------------------------------------------
> Andy Shevchenko (1):
>       lockdep: Move hlock_equal() to the respective ifdeffery
> 
> Waiman Long (2):
>       locking/lockdep: Prevent abuse of lockdep subclass
>       locking/lockdep: Add # of dynamic keys stat to /proc/lockdep_stats
> 
>  kernel/locking/lockdep.c           | 76 ++++++++++++++++++++------------------
>  kernel/locking/lockdep_internals.h |  1 +
>  kernel/locking/lockdep_proc.c      |  2 +
>  3 files changed, 44 insertions(+), 35 deletions(-)

Thanks, applied to the locking tree (tip:locking/core).

	Ingo

[tip: locking/core] locking/lockdep: Add number of dynamic keys to /proc/lockdep_stats

[tip-bot2 for Waiman Long]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     cdb7d2d68cde6145a06a56c9d5d5d917297501c6
Gitweb:        https://git.kernel.org/tip/cdb7d2d68cde6145a06a56c9d5d5d917297501c6
Author:        Waiman Long <longman@redhat.com>
AuthorDate:    Mon, 05 May 2025 21:20:49 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 06 May 2025 18:34:43 +02:00

locking/lockdep: Add number of dynamic keys to /proc/lockdep_stats

There have been recent reports about running out of lockdep keys:

	MAX_LOCKDEP_KEYS too low!

One possible reason is that too many dynamic keys have been registered.
A possible culprit is the lockdep_register_key() call in qdisc_alloc()
of net/sched/sch_generic.c.

Currently, there is no way to find out how many dynamic keys have been
registered. Add such a stat to the /proc/lockdep_stats to get better
clarity.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Bill Wendling <morbo@google.com>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20250506042049.50060-4-boqun.feng@gmail.com
---
 kernel/locking/lockdep.c           | 3 +++
 kernel/locking/lockdep_internals.h | 1 +
 kernel/locking/lockdep_proc.c      | 2 ++
 3 files changed, 6 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 050dbe9..dd2bbf7 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -219,6 +219,7 @@ static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES);
 static struct hlist_head lock_keys_hash[KEYHASH_SIZE];
 unsigned long nr_lock_classes;
 unsigned long nr_zapped_classes;
+unsigned long nr_dynamic_keys;
 unsigned long max_lock_class_idx;
 struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
 DECLARE_BITMAP(lock_classes_in_use, MAX_LOCKDEP_KEYS);
@@ -1238,6 +1239,7 @@ void lockdep_register_key(struct lock_class_key *key)
 			goto out_unlock;
 	}
 	hlist_add_head_rcu(&key->hash_entry, hash_head);
+	nr_dynamic_keys++;
 out_unlock:
 	graph_unlock();
 restore_irqs:
@@ -6609,6 +6611,7 @@ void lockdep_unregister_key(struct lock_class_key *key)
 		pf = get_pending_free();
 		__lockdep_free_key_range(pf, key, 1);
 		need_callback = prepare_call_rcu_zapped(pf);
+		nr_dynamic_keys--;
 	}
 	lockdep_unlock();
 	raw_local_irq_restore(flags);
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 20f9ef5..82156ca 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -138,6 +138,7 @@ extern unsigned long nr_lock_classes;
 extern unsigned long nr_zapped_classes;
 extern unsigned long nr_zapped_lock_chains;
 extern unsigned long nr_list_entries;
+extern unsigned long nr_dynamic_keys;
 long lockdep_next_lockchain(long i);
 unsigned long lock_chain_count(void);
 extern unsigned long nr_stack_trace_entries;
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index 6db0f43..b52c07c 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -286,6 +286,8 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
 #endif
 	seq_printf(m, " lock-classes:                  %11lu [max: %lu]\n",
 			nr_lock_classes, MAX_LOCKDEP_KEYS);
+	seq_printf(m, " dynamic-keys:                  %11lu\n",
+			nr_dynamic_keys);
 	seq_printf(m, " direct dependencies:           %11lu [max: %lu]\n",
 			nr_list_entries, MAX_LOCKDEP_ENTRIES);
 	seq_printf(m, " indirect dependencies:         %11lu\n",

[tip: locking/core] locking/lockdep: Prevent abuse of lockdep subclass

[tip-bot2 for Waiman Long]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     6a1a219f535a437eb12a06d8cef2518e58654beb
Gitweb:        https://git.kernel.org/tip/6a1a219f535a437eb12a06d8cef2518e58654beb
Author:        Waiman Long <longman@redhat.com>
AuthorDate:    Mon, 05 May 2025 21:20:48 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 06 May 2025 18:34:35 +02:00

locking/lockdep: Prevent abuse of lockdep subclass

To catch the code trying to use a subclass value >= MAX_LOCKDEP_SUBCLASSES (8),
add a DEBUG_LOCKS_WARN_ON() statement to notify the users that such a
large value is not allowed.

[ boqun: Reword the commit log with a more objective tone ]

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Bill Wendling <morbo@google.com>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20250506042049.50060-3-boqun.feng@gmail.com
---
 kernel/locking/lockdep.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 546e928..050dbe9 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5101,6 +5101,9 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 		lockevent_inc(lockdep_nocheck);
 	}
 
+	if (DEBUG_LOCKS_WARN_ON(subclass >= MAX_LOCKDEP_SUBCLASSES))
+		return 0;
+
 	if (subclass < NR_LOCKDEP_CACHING_CLASSES)
 		class = lock->class_cache[subclass];
 	/*

[tip: locking/core] locking/lockdep: Move hlock_equal() to the respective #ifdeffery

[tip-bot2 for Andy Shevchenko]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     96ca1830e1219eda431702eb9a74225e8fe3ccc0
Gitweb:        https://git.kernel.org/tip/96ca1830e1219eda431702eb9a74225e8fe3ccc0
Author:        Andy Shevchenko <andriy.shevchenko@linux.intel.com>
AuthorDate:    Mon, 05 May 2025 21:20:47 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 06 May 2025 18:34:31 +02:00

locking/lockdep: Move hlock_equal() to the respective #ifdeffery

When hlock_equal() is unused, it prevents kernel builds with clang,
`make W=1` and CONFIG_WERROR=y, CONFIG_LOCKDEP=y and
CONFIG_LOCKDEP_SMALL=n:

  lockdep.c:2005:20: error: unused function 'hlock_equal' [-Werror,-Wunused-function]

Fix this by moving the function to the respective existing ifdeffery
for its the only user.

See also:

  6863f5643dd7 ("kbuild: allow Clang to find unused static inline functions for W=1 build")

Fixes: 68e305678583 ("lockdep: Adjust check_redundant() for recursive read change")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Bill Wendling <morbo@google.com>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20250506042049.50060-2-boqun.feng@gmail.com
---
 kernel/locking/lockdep.c | 70 +++++++++++++++++++--------------------
 1 file changed, 35 insertions(+), 35 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 58d78a3..546e928 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1977,41 +1977,6 @@ print_circular_bug_header(struct lock_list *entry, unsigned int depth,
 }
 
 /*
- * We are about to add A -> B into the dependency graph, and in __bfs() a
- * strong dependency path A -> .. -> B is found: hlock_class equals
- * entry->class.
- *
- * If A -> .. -> B can replace A -> B in any __bfs() search (means the former
- * is _stronger_ than or equal to the latter), we consider A -> B as redundant.
- * For example if A -> .. -> B is -(EN)-> (i.e. A -(E*)-> .. -(*N)-> B), and A
- * -> B is -(ER)-> or -(EN)->, then we don't need to add A -> B into the
- * dependency graph, as any strong path ..-> A -> B ->.. we can get with
- * having dependency A -> B, we could already get a equivalent path ..-> A ->
- * .. -> B -> .. with A -> .. -> B. Therefore A -> B is redundant.
- *
- * We need to make sure both the start and the end of A -> .. -> B is not
- * weaker than A -> B. For the start part, please see the comment in
- * check_redundant(). For the end part, we need:
- *
- * Either
- *
- *     a) A -> B is -(*R)-> (everything is not weaker than that)
- *
- * or
- *
- *     b) A -> .. -> B is -(*N)-> (nothing is stronger than this)
- *
- */
-static inline bool hlock_equal(struct lock_list *entry, void *data)
-{
-	struct held_lock *hlock = (struct held_lock *)data;
-
-	return hlock_class(hlock) == entry->class && /* Found A -> .. -> B */
-	       (hlock->read == 2 ||  /* A -> B is -(*R)-> */
-		!entry->only_xr); /* A -> .. -> B is -(*N)-> */
-}
-
-/*
  * We are about to add B -> A into the dependency graph, and in __bfs() a
  * strong dependency path A -> .. -> B is found: hlock_class equals
  * entry->class.
@@ -2916,6 +2881,41 @@ static inline bool usage_skip(struct lock_list *entry, void *mask)
 
 #ifdef CONFIG_LOCKDEP_SMALL
 /*
+ * We are about to add A -> B into the dependency graph, and in __bfs() a
+ * strong dependency path A -> .. -> B is found: hlock_class equals
+ * entry->class.
+ *
+ * If A -> .. -> B can replace A -> B in any __bfs() search (means the former
+ * is _stronger_ than or equal to the latter), we consider A -> B as redundant.
+ * For example if A -> .. -> B is -(EN)-> (i.e. A -(E*)-> .. -(*N)-> B), and A
+ * -> B is -(ER)-> or -(EN)->, then we don't need to add A -> B into the
+ * dependency graph, as any strong path ..-> A -> B ->.. we can get with
+ * having dependency A -> B, we could already get a equivalent path ..-> A ->
+ * .. -> B -> .. with A -> .. -> B. Therefore A -> B is redundant.
+ *
+ * We need to make sure both the start and the end of A -> .. -> B is not
+ * weaker than A -> B. For the start part, please see the comment in
+ * check_redundant(). For the end part, we need:
+ *
+ * Either
+ *
+ *     a) A -> B is -(*R)-> (everything is not weaker than that)
+ *
+ * or
+ *
+ *     b) A -> .. -> B is -(*N)-> (nothing is stronger than this)
+ *
+ */
+static inline bool hlock_equal(struct lock_list *entry, void *data)
+{
+	struct held_lock *hlock = (struct held_lock *)data;
+
+	return hlock_class(hlock) == entry->class && /* Found A -> .. -> B */
+	       (hlock->read == 2 ||  /* A -> B is -(*R)-> */
+		!entry->only_xr); /* A -> .. -> B is -(*N)-> */
+}
+
+/*
  * Check that the dependency graph starting at <src> can lead to
  * <target> or not. If it can, <src> -> <target> dependency is already
  * in the graph.