This is a note to let you know that I've just added the patch titled
netfs/fscache: Add a memory barrier for FSCACHE_VOLUME_CREATING
to the 6.12-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:
netfs-fscache-add-a-memory-barrier-for-fscache_volum.patch
and it can be found in the queue-6.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 60753bc926a5140b23f4aa42ae3a4e0bbb29ddd4
Author: Zizhi Wo <wozizhi@xxxxxxxxxx>
Date: Thu Nov 7 19:06:49 2024 +0800
netfs/fscache: Add a memory barrier for FSCACHE_VOLUME_CREATING
[ Upstream commit 22f9400a6f3560629478e0a64247b8fcc811a24d ]
In fscache_create_volume(), there is a missing memory barrier between the
bit-clearing operation and the wake-up operation. This may cause a
situation where, after a wake-up, the bit-clearing operation hasn't been
detected yet, leading to an indefinite wait. The triggering process is as
follows:
[cookie1] [cookie2] [volume_work]
fscache_perform_lookup
fscache_create_volume
fscache_perform_lookup
fscache_create_volume
fscache_create_volume_work
cachefiles_acquire_volume
clear_and_wake_up_bit
test_and_set_bit
test_and_set_bit
goto maybe_wait
goto no_wait
In the above process, cookie1 and cookie2 has the same volume. When cookie1
enters the -no_wait- process, it will clear the bit and wake up the waiting
process. If a barrier is missing, it may cause cookie2 to remain in the
-wait- process indefinitely.
In commit 3288666c7256 ("fscache: Use clear_and_wake_up_bit() in
fscache_create_volume_work()"), barriers were added to similar operations
in fscache_create_volume_work(), but fscache_create_volume() was missed.
By combining the clear and wake operations into clear_and_wake_up_bit() to
fix this issue.
Fixes: bfa22da3ed65 ("fscache: Provide and use cache methods to lookup/create/free a volume")
Signed-off-by: Zizhi Wo <wozizhi@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20241107110649.3980193-6-wozizhi@xxxxxxxxxx
Acked-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/netfs/fscache_volume.c b/fs/netfs/fscache_volume.c
index cb75c07b5281a..ced14ac78cc1c 100644
--- a/fs/netfs/fscache_volume.c
+++ b/fs/netfs/fscache_volume.c
@@ -322,8 +322,7 @@ void fscache_create_volume(struct fscache_volume *volume, bool wait)
}
return;
no_wait:
- clear_bit_unlock(FSCACHE_VOLUME_CREATING, &volume->flags);
- wake_up_bit(&volume->flags, FSCACHE_VOLUME_CREATING);
+ clear_and_wake_up_bit(FSCACHE_VOLUME_CREATING, &volume->flags);
}
/*
