dm: fix limits initialization when there are no data devices

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 <michaelc@cs.wisc.edu>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # v3.6+
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 0890abd9dffa..1016c14c28a0 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2446,7 +2446,7 @@ static void dm_queue_flush(struct mapped_device *md)
  */
 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 mapped_device *md, struct dm_table *table)
                 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);