mirrors/linux-stable
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git synced 2024-09-27 21:03:32 +00:00
Code Issues Releases Wiki Activity

locking/seqlock: Do the lockdep annotation before locking in do_write_seqcount_begin_nested()

Browse source 
[ Upstream commit 41b43b6c6e ]

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: 1ca7d67cf5 ("seqcount: Add lockdep functionality to seqcount/seqlock structures")
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230920104627._DTHgPyA@linutronix.de

Closes: https://lore.kernel.org/20230621130641.-5iueY1I@linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Sebastian Andrzej Siewior 2023-09-20 12:46:27 +02:00 committed by Greg Kroah-Hartman
parent a70dbdede0
commit 07b569051f
1 changed files with 1 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
include/linux/seqlock.h
View file

@ -516,8 +516,8 @@ 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);
}
/**