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

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>
Cc: stable@vger.kernel.org

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 9d7275fb541a..6e702fc69a83 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -779,6 +779,10 @@ 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);
         }