From 621d101a7ebb7965ee3332e4e6e8d17bdd8f0555 Mon Sep 17 00:00:00 2001
From: Mike Snitzer <snitzer@redhat.com>
Date: Wed, 25 Jan 2017 16:24:52 +0100
Subject: 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
--- 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);
 	}
-- 
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