dm rq: cope with DM device destruction while in dm_old_request_fn()

commit 4087a1fffe38106e10646606a27f10d40451862d upstream.

Fixes a crash in dm_table_find_target() due to a NULL struct dm_table
being passed from dm_old_request_fn() that races with DM device
destruction.

Reported-by: artem@flashgrid.io
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 31a89c8..2c96542 100644 (file)
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -804,6 +804,10 @@ static void dm_old_request_fn(struct request_queue *q)
                int srcu_idx;
                struct dm_table *map = dm_get_live_table(md, &srcu_idx);
 
+               if (unlikely(!map)) {
+                       dm_put_live_table(md, srcu_idx);
+                       return;
+               }
                ti = dm_table_find_target(map, pos);
                dm_put_live_table(md, srcu_idx);
        }