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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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34
kernel/locking/lockdep.c
View File

@@ -5693,6 +5693,40 @@ void lock_release(struct lockdep_map *lock, unsigned long ip)
}
EXPORT_SYMBOL_GPL(lock_release);
/*
* lock_sync() - A special annotation for synchronize_{s,}rcu()-like API.
*
* No actual critical section is created by the APIs annotated with this: these
* APIs are used to wait for one or multiple critical sections (on other CPUs
* or threads), and it means that calling these APIs inside these critical
* sections is potential deadlock.
*
* This annotation acts as an acquire+release annotation pair with hardirqoff
* being 1. Since there's no critical section, no interrupt can create extra
* dependencies "inside" the annotation, hardirqoff == 1 allows us to avoid
* false positives.
*/
void lock_sync(struct lockdep_map *lock, unsigned subclass, int read,
int check, struct lockdep_map *nest_lock, unsigned long ip)
{
unsigned long flags;
if (unlikely(!lockdep_enabled()))
return;
raw_local_irq_save(flags);
check_flags(flags);
lockdep_recursion_inc();
__lock_acquire(lock, subclass, 0, read, check, 1, nest_lock, ip, 0, 0);
if (__lock_release(lock, ip))
check_chain_key(current);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(lock_sync);
noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
{
unsigned long flags;