Revert "blk-mq: fix hctx/ctx kobject use-after-free"

This reverts commit 76d697d1.

The commit 76d697d1 causes general protection fault
reported from Bart Van Assche:

	https://lkml.org/lkml/2015/1/28/334Reported-by: NBart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

block/blk-mq-sysfs.c

@@ -15,26 +15,6 @@
 
 static void blk_mq_sysfs_release(struct kobject *kobj)
 {
-	struct request_queue *q;
-
-	q = container_of(kobj, struct request_queue, mq_kobj);
-	free_percpu(q->queue_ctx);
-}
-
-static void blk_mq_ctx_release(struct kobject *kobj)
-{
-	struct blk_mq_ctx *ctx;
-
-	ctx = container_of(kobj, struct blk_mq_ctx, kobj);
-	kobject_put(&ctx->queue->mq_kobj);
-}
-
-static void blk_mq_hctx_release(struct kobject *kobj)
-{
-	struct blk_mq_hw_ctx *hctx;
-
-	hctx = container_of(kobj, struct blk_mq_hw_ctx, kobj);
-	kfree(hctx);
 }
 
 struct blk_mq_ctx_sysfs_entry {
@@ -338,13 +318,13 @@ static struct kobj_type blk_mq_ktype = {
 static struct kobj_type blk_mq_ctx_ktype = {
 	.sysfs_ops	= &blk_mq_sysfs_ops,
 	.default_attrs	= default_ctx_attrs,
-	.release	= blk_mq_ctx_release,
+	.release	= blk_mq_sysfs_release,
 };
 
 static struct kobj_type blk_mq_hw_ktype = {
 	.sysfs_ops	= &blk_mq_hw_sysfs_ops,
 	.default_attrs	= default_hw_ctx_attrs,
-	.release	= blk_mq_hctx_release,
+	.release	= blk_mq_sysfs_release,
 };
 
 static void blk_mq_unregister_hctx(struct blk_mq_hw_ctx *hctx)
@@ -375,7 +355,6 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx)
 		return ret;
 
 	hctx_for_each_ctx(hctx, ctx, i) {
-		kobject_get(&q->mq_kobj);
 		ret = kobject_add(&ctx->kobj, &hctx->kobj, "cpu%u", ctx->cpu);
 		if (ret)
 			break;

block/blk-mq.c

@@ -1641,8 +1641,10 @@ 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,
@@ -2000,9 +2002,11 @@ 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;