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 3288666c72 ("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: bfa22da3ed ("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>
Export fscache_put_volume() and add fscache_try_get_volume()
helper function to allow cachefiles to get/put fscache_volume
via linux/fscache-cache.h.
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Link: https://lore.kernel.org/r/20240628062930.2467993-2-libaokun@huaweicloud.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Instead of inventing a custom way to conditionally enable debugging,
just make use of pr_debug(), which also has dynamic debugging facilities
and is more likely known to someone who hunts a problem in the netfs
code. Also drop the module parameter netfs_debug which didn't have any
effect without further source changes. (The variable netfs_debug was
only used in #ifdef blocks for cpp vars that don't exist; Note that
CONFIG_NETFS_DEBUG isn't settable via kconfig, a variable with that name
never existed in the mainline and is probably just taken over (and
renamed) from similar custom debug logging implementations.)
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
Link: https://lore.kernel.org/r/20240608151352.22860-2-ukleinek@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
There's a problem with dependencies between netfslib and fscache as each
wants to access some functions of the other. Deal with this by moving
fs/fscache/* into fs/netfs/ and renaming those files to begin with
"fscache-".
For the moment, the moved files are changed as little as possible and an
fscache module is still built. A subsequent patch will integrate them.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Christian Brauner <christian@brauner.io>
cc: linux-fsdevel@vger.kernel.org
cc: linux-cachefs@redhat.com
