dm table: fix 'all_blk_mq' inconsistency when an empty table is loaded

An earlier DM multipath table could have been build ontop of underlying
devices that were all using blk-mq.  In that case, if that active
multipath table is replaced with an empty DM multipath table (that
reflects all paths have failed) then it is important that the
'all_blk_mq' state of the active table is transfered to the new empty DM
table.  Otherwise dm-rq.c:dm_old_prep_tio() will incorrectly clone a
request that isn't needed by the DM multipath target when it is to issue
IO to an underlying blk-mq device.

Fixes: e83068a5 ("dm mpath: add optional "queue_mode" feature")
Cc: stable@vger.kernel.org # 4.8+
Reported-by: Bart Van Assche <bart.vanassche@sandisk.com>
Tested-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index c4b53b3..53b817b 100644 (file)
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -924,12 +924,6 @@ static int dm_table_determine_type(struct dm_table *t)
 
        BUG_ON(!request_based); /* No targets in this table */
 
-       if (list_empty(devices) && __table_type_request_based(live_md_type)) {
-               /* inherit live MD type */
-               t->type = live_md_type;
-               return 0;
-       }
-
        /*
         * The only way to establish DM_TYPE_MQ_REQUEST_BASED is by
         * having a compatible target use dm_table_set_type.
@@ -948,6 +942,19 @@ verify_rq_based:
                return -EINVAL;
        }
 
+       if (list_empty(devices)) {
+               int srcu_idx;
+               struct dm_table *live_table = dm_get_live_table(t->md, &srcu_idx);
+
+               /* inherit live table's type and all_blk_mq */
+               if (live_table) {
+                       t->type = live_table->type;
+                       t->all_blk_mq = live_table->all_blk_mq;
+               }
+               dm_put_live_table(t->md, srcu_idx);
+               return 0;
+       }
+
        /* Non-request-stackable devices can't be used for request-based dm */
        list_for_each_entry(dd, devices, list) {
                struct request_queue *q = bdev_get_queue(dd->dm_dev->bdev);