The patch titled
Subject: seqlock: do the lockdep annotation before locking in do_write_seqcount_begin_nested()
has been added to the -mm mm-unstable branch. Its filename is
seqlock-do-the-lockdep-annotation-before-locking-in-do_write_seqcount_begin_nested.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/seqlock-do-the-lockdep-annotation-before-locking-in-do_write_seqcount_begin_nested.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Subject: seqlock: do the lockdep annotation before locking in do_write_seqcount_begin_nested()
Date: Fri, 23 Jun 2023 19:12:31 +0200
Patch series "seqlock,mm: lockdep annotation + write_seqlock_irqsave()",
v2.
This patch (of 2):
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).
Link: https://lkml.kernel.org/r/20230623171232.892937-2-bigeasy@xxxxxxxxxxxxx
Fixes: 1ca7d67cf5d5a ("seqcount: Add lockdep functionality to seqcount/seqlock structures")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/20230621130641.-5iueY1I@xxxxxxxxxxxxx
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: John Ogness <john.ogness@xxxxxxxxxxxxx>
Cc: Luis Claudio R. Goncalves <lgoncalv@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/seqlock.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/include/linux/seqlock.h~seqlock-do-the-lockdep-annotation-before-locking-in-do_write_seqcount_begin_nested
+++ a/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);
}
/**
_
Patches currently in -mm which might be from bigeasy@xxxxxxxxxxxxx are
seqlock-do-the-lockdep-annotation-before-locking-in-do_write_seqcount_begin_nested.patch
mm-page_alloc-use-write_seqlock_irqsave-instead-write_seqlock-local_irq_save.patch
