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authorRoman Gushchin <guro@fb.com>2021-06-28 19:35:44 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-06-29 10:53:47 -0700
commit592fa002180af3425ba962b8e74edd680f0ec77b (patch)
tree66bed02c0252d8629f4e85b5fa003e7cae40e420 /fs/fs-writeback.c
parent4ade5867b4b878b00a4526b8621442f9442536ce (diff)
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.c6
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