blk-mq: don't touch ->tagset in blk_mq_get_sq_hctx

blk_mq_run_hw_queues() could be run when there isn't queued request and
after queue is cleaned up, at that time tagset is freed, because tagset
lifetime is covered by driver, and often freed after blk_cleanup_queue()
returns.

So don't touch ->tagset for figuring out current default hctx by the mapping
built in request queue, so use-after-free on tagset can be avoided. Meantime
this way should be fast than retrieving mapping from tagset.

Cc: "yukuai (C)" <[email protected]>
Cc: Jan Kara <[email protected]>
Fixes: b6e68ee ("blk-mq: Improve performance of non-mq IO schedulers with multiple HW queues")
Signed-off-by: Ming Lei <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

block/blk-mq.c

@@ -2130,17 +2130,16 @@ static bool blk_mq_has_sqsched(struct request_queue *q)
  */
 static struct blk_mq_hw_ctx *blk_mq_get_sq_hctx(struct request_queue *q)
 {
-	struct blk_mq_hw_ctx *hctx;
-
+	struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
 	/*
 	 * If the IO scheduler does not respect hardware queues when
 	 * dispatching, we just don't bother with multiple HW queues and
 	 * dispatch from hctx for the current CPU since running multiple queues
 	 * just causes lock contention inside the scheduler and pointless cache
 	 * bouncing.
 	 */
-	hctx = blk_mq_map_queue_type(q, HCTX_TYPE_DEFAULT,
-				     raw_smp_processor_id());
+	struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, 0, ctx);
+
 	if (!blk_mq_hctx_stopped(hctx))
 		return hctx;
 	return NULL;