diff options
| author | Roman Gushchin <guro@fb.com> | 2021-06-28 19:35:44 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2021-06-29 10:53:47 -0700 |
| commit | 592fa002180af3425ba962b8e74edd680f0ec77b (patch) | |
| tree | 66bed02c0252d8629f4e85b5fa003e7cae40e420 /fs/fs-writeback.c | |
| parent | 4ade5867b4b878b00a4526b8621442f9442536ce (diff) | |
| download | lwn-592fa002180af3425ba962b8e74edd680f0ec77b.tar.gz lwn-592fa002180af3425ba962b8e74edd680f0ec77b.zip | |
writeback, cgroup: add smp_mb() to cgroup_writeback_umount()
A full memory barrier is required between clearing SB_ACTIVE flag in
generic_shutdown_super() and checking isw_nr_in_flight in
cgroup_writeback_umount(), otherwise a new switch operation might be
scheduled after atomic_read(&isw_nr_in_flight) returned 0. This would
result in a non-flushed isw_wq, and a potential crash.
The problem hasn't yet been seen in the real life and was discovered by
Jan Kara by looking into the code.
Link: https://lkml.kernel.org/r/20210608230225.2078447-3-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Jan Kara <jack@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/fs-writeback.c')
| -rw-r--r-- | fs/fs-writeback.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index bd99890599e0..3564efcc4b78 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1000,6 +1000,12 @@ out_bdi_put: */ void cgroup_writeback_umount(void) { + /* + * SB_ACTIVE should be reliably cleared before checking + * isw_nr_in_flight, see generic_shutdown_super(). + */ + smp_mb(); + if (atomic_read(&isw_nr_in_flight)) { /* * Use rcu_barrier() to wait for all pending callbacks to |