Patch "dm table: fix 'all_blk_mq' inconsistency when an empty table is loaded" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
dm-table-fix-all_blk_mq-inconsistency-when-an-empty-table-is-loaded.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Mike Snitzer <[email protected]>
Date: Wed, 23 Nov 2016 13:51:09 -0500
Subject: dm table: fix 'all_blk_mq' inconsistency when an empty table is loaded

From: Mike Snitzer <[email protected]>

commit 6936c12cf809850180b24947271b8f068fdb15e9 upstream.

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.

---
 drivers/md/dm-table.c |   19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

@@ -924,12 +924,6 @@ static int dm_table_determine_type(struc
 
 	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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/dm-raid-fix-discard-support-regression.patch queue-4.8/dm-rq-fix-a-race-condition-in-rq_completed.patch queue-4.8/dm-flakey-return-einval-on-interval-bounds-error-in-flakey_ctr.patch queue-4.8/dm-space-map-metadata-fix-struct-sm_metadata-leak-on-failed-create.patch queue-4.8/dm-table-fix-all_blk_mq-inconsistency-when-an-empty-table-is-loaded.patch queue-4.8/dm-crypt-mark-key-as-invalid-until-properly-loaded.patch queue-4.8/dm-table-an-all_blk_mq-table-must-be-loaded-for-a-blk-mq-dm-device.patch