blk-mq: release mq's kobjects in blk_release_queue()

The kobject memory inside blk-mq hctx/ctx shouldn't have been freed
before the kobject is released because driver core can access it freely
before its release.

We can't do that in all ctx/hctx/mq_kobj's release handler because
it can be run before blk_cleanup_queue().

Given mq_kobj shouldn't have been introduced, this patch simply moves
mq's release into blk_release_queue().
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-mq.c

@@ -1641,10 +1641,8 @@ static void blk_mq_free_hw_queues(struct request_queue *q,
 	struct blk_mq_hw_ctx *hctx;
 	unsigned int i;
 
-	queue_for_each_hw_ctx(q, hctx, i) {
+	queue_for_each_hw_ctx(q, hctx, i)
 		free_cpumask_var(hctx->cpumask);
-		kfree(hctx);
-	}
 }
 
 static int blk_mq_init_hctx(struct request_queue *q,
@@ -1869,6 +1867,27 @@ static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set,
 	mutex_unlock(&set->tag_list_lock);
 }
 
+/*
+ * It is the actual release handler for mq, but we do it from
+ * request queue's release handler for avoiding use-after-free
+ * and headache because q->mq_kobj shouldn't have been introduced,
+ * but we can't group ctx/kctx kobj without it.
+ */
+void blk_mq_release(struct request_queue *q)
+{
+	struct blk_mq_hw_ctx *hctx;
+	unsigned int i;
+
+	/* hctx kobj stays in hctx */
+	queue_for_each_hw_ctx(q, hctx, i)
+		kfree(hctx);
+
+	kfree(q->queue_hw_ctx);
+
+	/* ctx kobj stays in queue_ctx */
+	free_percpu(q->queue_ctx);
+}
+
 struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)
 {
 	struct blk_mq_hw_ctx **hctxs;
@@ -2002,12 +2021,8 @@ void blk_mq_free_queue(struct request_queue *q)
 
 	percpu_ref_exit(&q->mq_usage_counter);
 
-	free_percpu(q->queue_ctx);
-	kfree(q->queue_hw_ctx);
 	kfree(q->mq_map);
 
-	q->queue_ctx = NULL;
-	q->queue_hw_ctx = NULL;
 	q->mq_map = NULL;
 
 	mutex_lock(&all_q_mutex);

block/blk-mq.h

@@ -62,6 +62,8 @@ extern void blk_mq_sysfs_unregister(struct request_queue *q);
 
 extern void blk_mq_rq_timed_out(struct request *req, bool reserved);
 
+void blk_mq_release(struct request_queue *q);
+
 /*
  * Basic implementation of sparser bitmap, allowing the user to spread
  * the bits over more cachelines.

block/blk-sysfs.c

@@ -517,6 +517,8 @@ static void blk_release_queue(struct kobject *kobj)
 
 	if (!q->mq_ops)
 		blk_free_flush_queue(q->fq);
+	else
+		blk_mq_release(q);
 
 	blk_trace_shutdown(q);