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locking/lockdep: Introduce lock_sync()

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Currently, functions like synchronize_srcu() do not have lockdep
annotations resembling those of other write-side locking primitives.
Such annotations might look as follows:

	lock_acquire();
	lock_release();

Such annotations would tell lockdep that synchronize_srcu() acts like
an empty critical section that waits for other (read-side) critical
sections to finish.  This would definitely catch some deadlock, but
as pointed out by Paul Mckenney [1], this could also introduce false
positives because of irq-safe/unsafe detection.  Of course, there are
tricks could help with this:

	might_sleep(); // Existing statement in __synchronize_srcu().
	if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
		local_irq_disable();
		lock_acquire();
		lock_release();
		local_irq_enable();
	}

But it would be better for lockdep to provide a separate annonation for
functions like synchronize_srcu(), so that people won't need to repeat
the ugly tricks above.

Therefore introduce lock_sync(), which is simply an lock+unlock
pair with no irq safe/unsafe deadlock check.  This works because the
to-be-annontated functions do not create real critical sections, and
there is therefore no way that irq can create extra dependencies.

[1]: https://lore.kernel.org/lkml/20180412021233.ewncg5jjuzjw3x62@tardis/

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
[ boqun: Fix typos reported by Davidlohr Bueso and Paul E. Mckenney ]
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
This commit is contained in:
Boqun Feng
2023-01-12 22:59:53 -08:00
parent fe15c26ee2
commit 2f1f043e7b
2 changed files with 39 additions and 0 deletions
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5
include/linux/lockdep.h
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@@ -268,6 +268,10 @@ extern void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
extern void lock_release(struct lockdep_map *lock, unsigned long ip);
extern void lock_sync(struct lockdep_map *lock, unsigned int subclass,
int read, int check, struct lockdep_map *nest_lock,
unsigned long ip);
/* lock_is_held_type() returns */
#define LOCK_STATE_UNKNOWN -1
#define LOCK_STATE_NOT_HELD 0
@@ -554,6 +558,7 @@ do { \
#define lock_map_acquire_read(l) lock_acquire_shared_recursive(l, 0, 0, NULL, _THIS_IP_)
#define lock_map_acquire_tryread(l) lock_acquire_shared_recursive(l, 0, 1, NULL, _THIS_IP_)
#define lock_map_release(l) lock_release(l, _THIS_IP_)
#define lock_map_sync(l) lock_sync(l, 0, 0, 1, NULL, _THIS_IP_)
#ifdef CONFIG_PROVE_LOCKING
# define might_lock(lock) \