6.6-stable review patch. If anyone has any objections, please let me know.
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From: Zizhi Wo wozizhi@huawei.com
[ 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@huawei.com Link: https://lore.kernel.org/r/20241107110649.3980193-6-wozizhi@huawei.com Acked-by: David Howells dhowells@redhat.com Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/fscache/volume.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/fs/fscache/volume.c b/fs/fscache/volume.c index cb75c07b5281a..ced14ac78cc1c 100644 --- a/fs/fscache/volume.c +++ b/fs/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); }
/*