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>
---
fs/netfs/fscache_volume.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/fs/netfs/fscache_volume.c b/fs/netfs/fscache_volume.c
index cb75c07b5281..ced14ac78cc1 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);
}
/*
--
2.39.2
