[PATCH 4.9 05/60] dm rq: cope with DM device destruction while in dm_old_request_fn()

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Snitzer <snitzer@xxxxxxxxxx>

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@xxxxxxxxxxxx
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/md/dm-rq.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -804,6 +804,10 @@ static void dm_old_request_fn(struct req
 		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);
 	}