dm mpath: flush keventd queue in destructor

commit 53b351f972a882ea8b6cdb19602535f1057c884a upstream.

The commit fe9cf30eb8186ef267d1868dc9f12f2d0f40835a moves dm table event
submission from kmultipath queue to kernel kevent queue to avoid a
deadlock.

There is a possibility of race condition because kevent queue is not flushed
in the multipath destructor. The scenario is:
- some event happens and is queued to keventd
- keventd thread is delayed due to scheuling latency or some other work
- multipath device is destroyed
- keventd now attempts to process work_struct that is residing in already
  released memory.

The patch flushes the keventd queue in multipath constructor.
I've already fixed similar bug in dm-raid1.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index f25bdebcb4ab01406be763d74632ff82d8f99c95..3a8f827e745593e30c64400681536f37ca2111f2 100644 (file)
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -847,6 +847,7 @@ static void multipath_dtr(struct dm_target *ti)
 
        flush_workqueue(kmpath_handlerd);
        flush_workqueue(kmultipathd);
+       flush_scheduled_work();
        free_multipath(m);
 }