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"

4 files changed, 27 insertions, 25 deletions

diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index 6774a0e69867..1630a20d5dcf 100644
--- a/block/blk-mq-sysfs.c
+++ b/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;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9ee3b87c4498..2390c5541e71 100644
--- a/block/blk-mq.c
+++ b/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);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 4f4f943c22c3..6a48c4c0d8a2 100644
--- a/block/blk-mq.h
+++ b/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.
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 935ea2aa0730..faaf36ade7eb 100644
--- a/block/blk-sysfs.c
+++ b/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);