[PATCH 4.9 049/177] blk-mq: Fix tagset reinit in the presence of cpu hot-unplug

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sagi Grimberg <sagi@xxxxxxxxxxx>


[ Upstream commit 0067d4b020ea07a58540acb2c5fcd3364bf326e0 ]

In case cpu was unplugged, we need to make sure not to assume
that the tags for that cpu are still allocated. so check
for null tags when reinitializing a tagset.

Reported-by: Yi Zhang <yizhan@xxxxxxxxxx>
Signed-off-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 block/blk-mq-tag.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -311,6 +311,9 @@ int blk_mq_reinit_tagset(struct blk_mq_t
 	for (i = 0; i < set->nr_hw_queues; i++) {
 		struct blk_mq_tags *tags = set->tags[i];
 
+		if (!tags)
+			continue;
+
 		for (j = 0; j < tags->nr_tags; j++) {
 			if (!tags->rqs[j])
 				continue;