blk-mq: move cancel of hctx->run_work to the front of blk_exit_queue

blk_exit_queue will free elevator_data, while blk_mq_run_work_fn
will access it. Move cancel of hctx->run_work to the front of
blk_exit_queue to avoid use-after-free.

Fixes: 1b97871b501f ("blk-mq: move cancel of hctx->run_work into blk_mq_hw_sysfs_release")
Signed-off-by: Yang Yang <[e-mail]>
Reviewed-by: Ming Lei <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

block/blk-mq-sysfs.c

···
 	struct blk_mq_hw_ctx *hctx = container_of(kobj, struct blk_mq_hw_ctx,
 						  kobj);
 
-	cancel_delayed_work_sync(&hctx->run_work);
-
 	if (hctx->flags & BLK_MQ_F_BLOCKING)
 		cleanup_srcu_struct(hctx->srcu);
 	blk_free_flush_queue(hctx->fq);

block/blk-sysfs.c

···
 
 	blk_free_queue_stats(q->stats);
 
-	if (queue_is_mq(q))
+	if (queue_is_mq(q)) {
+		struct blk_mq_hw_ctx *hctx;
+		int i;
+
 		cancel_delayed_work_sync(&q->requeue_work);
+
+		queue_for_each_hw_ctx(q, hctx, i)
+			cancel_delayed_work_sync(&hctx->run_work);
+	}
 
 	blk_exit_queue(q);