This is a note to let you know that I've just added the patch titled
jump_label: Fix the fix, brown paper bags galore
to the 6.6-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:
jump_label-fix-the-fix-brown-paper-bags-galore.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 7442172301401d6d88df59821daa4799802ac8f3
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed Jul 31 12:43:21 2024 +0200
jump_label: Fix the fix, brown paper bags galore
[ Upstream commit 224fa3552029a3d14bec7acf72ded8171d551b88 ]
Per the example of:
!atomic_cmpxchg(&key->enabled, 0, 1)
the inverse was written as:
atomic_cmpxchg(&key->enabled, 1, 0)
except of course, that while !old is only true for old == 0, old is
true for everything except old == 0.
Fix it to read:
atomic_cmpxchg(&key->enabled, 1, 0) == 1
such that only the 1->0 transition returns true and goes on to disable
the keys.
Fixes: 83ab38ef0a0b ("jump_label: Fix concurrency issues in static_key_slow_dec()")
Reported-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20240731105557.GY33588@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index eec802175ccc6..1ed269b2c4035 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -231,7 +231,7 @@ void static_key_disable_cpuslocked(struct static_key *key)
}
jump_label_lock();
- if (atomic_cmpxchg(&key->enabled, 1, 0))
+ if (atomic_cmpxchg(&key->enabled, 1, 0) == 1)
jump_label_update(key);
jump_label_unlock();
}
@@ -284,7 +284,7 @@ static void __static_key_slow_dec_cpuslocked(struct static_key *key)
return;
guard(mutex)(&jump_label_mutex);
- if (atomic_cmpxchg(&key->enabled, 1, 0))
+ if (atomic_cmpxchg(&key->enabled, 1, 0) == 1)
jump_label_update(key);
else
WARN_ON_ONCE(!static_key_slow_try_dec(key));
