This is a note to let you know that I've just added the patch titled
locking/seqlock: Do the lockdep annotation before locking in do_write_seqcount_begin_nested()
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
locking-seqlock-do-the-lockdep-annotation-before-loc.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 903286a67bee0861e2722bd1ab8bea07ca022b2f
Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Date: Wed Sep 20 12:46:27 2023 +0200
locking/seqlock: Do the lockdep annotation before locking in do_write_seqcount_begin_nested()
[ Upstream commit 41b43b6c6e30a832c790b010a06772e793bca193 ]
It was brought up by Tetsuo that the following sequence:
write_seqlock_irqsave()
printk_deferred_enter()
could lead to a deadlock if the lockdep annotation within
write_seqlock_irqsave() triggers.
The problem is that the sequence counter is incremented before the lockdep
annotation is performed. The lockdep splat would then attempt to invoke
printk() but the reader side, of the same seqcount, could have a
tty_port::lock acquired waiting for the sequence number to become even again.
The other lockdep annotations come before the actual locking because "we
want to see the locking error before it happens". There is no reason why
seqcount should be different here.
Do the lockdep annotation first then perform the locking operation (the
sequence increment).
Fixes: 1ca7d67cf5d5a ("seqcount: Add lockdep functionality to seqcount/seqlock structures")
Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230920104627._DTHgPyA@xxxxxxxxxxxxx
Closes: https://lore.kernel.org/20230621130641.-5iueY1I@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 3926e90279477..d778af83c8f36 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -512,8 +512,8 @@ do { \
static inline void do_write_seqcount_begin_nested(seqcount_t *s, int subclass)
{
- do_raw_write_seqcount_begin(s);
seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_);
+ do_raw_write_seqcount_begin(s);
}
/**
