From: Mike Christie <[email-masked]>

dm_calculate_queue_limits will first reset the provided limits to
defaults using blk_set_stacking_limits; whereby defeating the purpose of
retaining the original live table's limits -- as was intended via commit
3ae706561637331aa578e52bb89ecbba5edcb7a9 ("dm: retain table limits when
swapping to new table with no devices").

Fix this improper limits initialization (in the no data devices case) by
avoiding the call to dm_calculate_queue_limits.

[patch header revised by Mike Snitzer]

Signed-off-by: Mike Christie <[email-masked]>
Signed-off-by: Mike Snitzer <[email-masked]>
Cc: [email-masked] # v3.6+
Signed-off-by: Alasdair G Kergon <[email-masked]>

---

 drivers/md/dm.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

Index: linux/drivers/md/dm.c
===================================================================
--- linux.orig/drivers/md/dm.c
+++ linux/drivers/md/dm.c
@@ -2446,7 +2446,7 @@ static void dm_queue_flush(struct mapped
  */
 struct dm_table *dm_swap_table(struct mapped_device *md, struct dm_table *table)
 {
-	struct dm_table *live_map, *map = ERR_PTR(-EINVAL);
+	struct dm_table *live_map = NULL, *map = ERR_PTR(-EINVAL);
 	struct queue_limits limits;
 	int r;
 
@@ -2469,10 +2469,12 @@ struct dm_table *dm_swap_table(struct ma
 		dm_table_put(live_map);
 	}
 
-	r = dm_calculate_queue_limits(table, &limits);
-	if (r) {
-		map = ERR_PTR(r);
-		goto out;
+	if (!live_map) {
+		r = dm_calculate_queue_limits(table, &limits);
+		if (r) {
+			map = ERR_PTR(r);
+			goto out;
+		}
 	}
 
 	map = __bind(md, table, &limits);