Merge branch 'for-linus' of git://git.kernel.dk/linux-block

Pull final block layer fixes from Jens Axboe:
 "Unfortunately the hctx/ctx lifetime fix from last pull had some
  issues.  This pull request contains a revert of the problematic
  commit, and a proper rewrite of it.

  The rewrite has been tested by the users complaining about the
  regression, and it works fine now.  Additionally, I've run testing on
  all the blk-mq use cases for it and it passes.  So we should
  definitely get this into 3.19, to avoid regression for some cases"

* 'for-linus' of git://git.kernel.dk/linux-block:
  blk-mq: release mq's kobjects in blk_release_queue()
  Revert "blk-mq: fix hctx/ctx kobject use-after-free"

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

@@ -1867,6 +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;
@@ -2000,10 +2021,8 @@ void blk_mq_free_queue(struct request_queue *q)
 
 	percpu_ref_exit(&q->mq_usage_counter);
 
-	kfree(q->queue_hw_ctx);
 	kfree(q->mq_map);
 
-	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);