linux-kernel - [PATCH] lockdep: lockdep_set_notrack

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Date: Sun, 30 Jun 2024 01:10:37 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: linux-kernel@...r.kernel.org,
	linux-bcachefs@...r.kernel.org
Cc: Kent Overstreet <kent.overstreet@...ux.dev>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>,
	Boqun Feng <boqun.feng@...il.com>
Subject: [PATCH] lockdep: lockdep_set_notrack_class()

Add a new helper to disable lockdep tracking entirely for a given class.

This is needed for bcachefs, which takes too many btree node locks for
lockdep to track. Instead, we have a single lockdep_map for "btree_trans
has any btree nodes locked", which makes more since given that we have
centralized lock management and a cycle detector.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Will Deacon <will@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
---
 fs/bcachefs/btree_locking.c   | 2 +-
 include/linux/lockdep.h       | 4 ++++
 include/linux/lockdep_types.h | 1 +
 kernel/locking/lockdep.c      | 9 ++++++++-
 4 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/bcachefs/btree_locking.c b/fs/bcachefs/btree_locking.c
index 79057cde4c41..16834a6b4c3d 100644
--- a/fs/bcachefs/btree_locking.c
+++ b/fs/bcachefs/btree_locking.c
@@ -10,7 +10,7 @@ void bch2_btree_lock_init(struct btree_bkey_cached_common *b,
 			  enum six_lock_init_flags flags)
 {
 	__six_lock_init(&b->lock, "b->c.lock", &bch2_btree_node_lock_key, flags);
-	lockdep_set_novalidate_class(&b->lock);
+	lockdep_set_notrack_class(&b->lock);
 }
 
 #ifdef CONFIG_LOCKDEP
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 08b0d1d9d78b..b76f1bcd2f7f 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -181,6 +181,9 @@ static inline void lockdep_init_map(struct lockdep_map *lock, const char *name,
 #define lockdep_set_novalidate_class(lock) \
 	lockdep_set_class_and_name(lock, &__lockdep_no_validate__, #lock)
 
+#define lockdep_set_notrack_class(lock) \
+	lockdep_set_class_and_name(lock, &__lockdep_no_track__, #lock)
+
 /*
  * Compare locking classes
  */
@@ -338,6 +341,7 @@ static inline void lockdep_set_selftest_task(struct task_struct *task)
 #define lockdep_set_subclass(lock, sub)		do { } while (0)
 
 #define lockdep_set_novalidate_class(lock) do { } while (0)
+#define lockdep_set_notrack_class(lock) do { } while (0)
 
 /*
  * We don't define lockdep_match_class() and lockdep_match_key() for !LOCKDEP
diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
index 70d30d40ea4a..9f361d3ab9d9 100644
--- a/include/linux/lockdep_types.h
+++ b/include/linux/lockdep_types.h
@@ -80,6 +80,7 @@ struct lock_class_key {
 };
 
 extern struct lock_class_key __lockdep_no_validate__;
+extern struct lock_class_key __lockdep_no_track__;
 
 struct lock_trace;
 
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 151bd3de5936..b6bb9fcd992a 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4918,6 +4918,9 @@ EXPORT_SYMBOL_GPL(lockdep_init_map_type);
 struct lock_class_key __lockdep_no_validate__;
 EXPORT_SYMBOL_GPL(__lockdep_no_validate__);
 
+struct lock_class_key __lockdep_no_track__;
+EXPORT_SYMBOL_GPL(__lockdep_no_track__);
+
 #ifdef CONFIG_PROVE_LOCKING
 void lockdep_set_lock_cmp_fn(struct lockdep_map *lock, lock_cmp_fn cmp_fn,
 			     lock_print_fn print_fn)
@@ -5002,6 +5005,9 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 	if (unlikely(!debug_locks))
 		return 0;
 
+	if (unlikely(lock->key == &__lockdep_no_track__))
+		return 0;
+
 	if (!prove_locking || lock->key == &__lockdep_no_validate__)
 		check = 0;
 
@@ -5764,7 +5770,8 @@ void lock_release(struct lockdep_map *lock, unsigned long ip)
 
 	trace_lock_release(lock, ip);
 
-	if (unlikely(!lockdep_enabled()))
+	if (unlikely(!lockdep_enabled() ||
+		     lock->key == &__lockdep_no_track__))
 		return;
 
 	raw_local_irq_save(flags);
-- 
2.45.2