[PATCH 2/2] blk-mq: fix CPU hotplug handling

[Ming Lei]

Firstly the hctx->tags have to be set as NULL if it is to be disabled
no matter if set->tags[i] is NULL or not in blk_mq_map_swqueue() because
shared tags can be freed already from another request queue.

The same situation has to be considered in blk_mq_hctx_cpu_online()
too.

Cc: <stable@xxxxxxxxxxxxxxx>
Reported-by: Dongsu Park <dongsu.park@xxxxxxxxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
---
 block/blk-mq.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 6804028..9da05b3 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1580,15 +1580,20 @@ static int blk_mq_hctx_cpu_online(struct blk_mq_hw_ctx *hctx, int cpu)
 {
 	struct request_queue *q = hctx->queue;
 	struct blk_mq_tag_set *set = q->tag_set;
+	struct blk_mq_tags	*tags = set->tags[hctx->queue_num];
 
-	if (set->tags[hctx->queue_num])
+	/* tags can be shared by more than one queues */
+	if (hctx->tags)
 		return NOTIFY_OK;
 
-	set->tags[hctx->queue_num] = blk_mq_init_rq_map(set, hctx->queue_num);
-	if (!set->tags[hctx->queue_num])
-		return NOTIFY_STOP;
+	if (!tags) {
+		tags = blk_mq_init_rq_map(set, hctx->queue_num);
+		if (!tags)
+			return NOTIFY_STOP;
+		set->tags[hctx->queue_num] = tags;
+	}
 
-	hctx->tags = set->tags[hctx->queue_num];
+	hctx->tags = tags;
 	return NOTIFY_OK;
 }
 
@@ -1813,8 +1818,8 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 			if (set->tags[i]) {
 				blk_mq_free_rq_map(set, set->tags[i], i);
 				set->tags[i] = NULL;
-				hctx->tags = NULL;
 			}
+			hctx->tags = NULL;
 			continue;
 		}
 
-- 
1.9.1

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