1 files changed, 36 insertions, 2 deletions

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 4e595ee8c915..8056c03a3382 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -266,7 +266,7 @@ static inline void blkg_get(struct blkcg_gq *blkg)
         blkg->refcnt++;
 }
 
-void __blkg_release(struct blkcg_gq *blkg);
+void __blkg_release_rcu(struct rcu_head *rcu);
 
 /**
  * blkg_put - put a blkg reference
@@ -279,9 +279,43 @@ static inline void blkg_put(struct blkcg_gq *blkg)
         lockdep_assert_held(blkg->q->queue_lock);
         WARN_ON_ONCE(blkg->refcnt <= 0);
         if (!--blkg->refcnt)
-                __blkg_release(blkg);
+                call_rcu(&blkg->rcu_head, __blkg_release_rcu);
 }
 
+struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg, struct request_queue *q,
+                               bool update_hint);
+
+/**
+ * blkg_for_each_descendant_pre - pre-order walk of a blkg's descendants
+ * @d_blkg: loop cursor pointing to the current descendant
+ * @pos_cgrp: used for iteration
+ * @p_blkg: target blkg to walk descendants of
+ *
+ * Walk @c_blkg through the descendants of @p_blkg.  Must be used with RCU
+ * read locked.  If called under either blkcg or queue lock, the iteration
+ * is guaranteed to include all and only online blkgs.  The caller may
+ * update @pos_cgrp by calling cgroup_rightmost_descendant() to skip
+ * subtree.
+ */
+#define blkg_for_each_descendant_pre(d_blkg, pos_cgrp, p_blkg)          \
+        cgroup_for_each_descendant_pre((pos_cgrp), (p_blkg)->blkcg->css.cgroup) \
+                if (((d_blkg) = __blkg_lookup(cgroup_to_blkcg(pos_cgrp), \
+                                              (p_blkg)->q, false)))
+
+/**
+ * blkg_for_each_descendant_post - post-order walk of a blkg's descendants
+ * @d_blkg: loop cursor pointing to the current descendant
+ * @pos_cgrp: used for iteration
+ * @p_blkg: target blkg to walk descendants of
+ *
+ * Similar to blkg_for_each_descendant_pre() but performs post-order
+ * traversal instead.  Synchronization rules are the same.
+ */
+#define blkg_for_each_descendant_post(d_blkg, pos_cgrp, p_blkg)         \
+        cgroup_for_each_descendant_post((pos_cgrp), (p_blkg)->blkcg->css.cgroup) \
+                if (((d_blkg) = __blkg_lookup(cgroup_to_blkcg(pos_cgrp), \
+                                              (p_blkg)->q, false)))
+
 /**
  * blk_get_rl - get request_list to use
  * @q: request_queue of interest