1 files changed, 65 insertions, 23 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 97266ebde975..3af0d4a61955 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -156,6 +156,17 @@ static void blkg_async_bio_workfn(struct work_struct *work)
 }
 
 /**
+ * blkcg_parent - get the parent of a blkcg
+ * @blkcg: blkcg of interest
+ *
+ * Return the parent blkcg of @blkcg.  Can be called anytime.
+ */
+static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)
+{
+	return css_to_blkcg(blkcg->css.parent);
+}
+
+/**
  * blkg_alloc - allocate a blkg
  * @blkcg: block cgroup the new blkg is associated with
  * @q: request_queue the new blkg is associated with
@@ -1016,25 +1027,6 @@ static struct cftype blkcg_legacy_files[] = {
  */
 
 /**
- * blkcg_css_offline - cgroup css_offline callback
- * @css: css of interest
- *
- * This function is called when @css is about to go away.  Here the cgwbs are
- * offlined first and only once writeback associated with the blkcg has
- * finished do we start step 2 (see above).
- */
-static void blkcg_css_offline(struct cgroup_subsys_state *css)
-{
-	struct blkcg *blkcg = css_to_blkcg(css);
-
-	/* this prevents anyone from attaching or migrating to this blkcg */
-	wb_blkcg_offline(blkcg);
-
-	/* put the base online pin allowing step 2 to be triggered */
-	blkcg_unpin_online(blkcg);
-}
-
-/**
  * blkcg_destroy_blkgs - responsible for shooting down blkgs
  * @blkcg: blkcg of interest
  *
@@ -1045,7 +1037,7 @@ static void blkcg_css_offline(struct cgroup_subsys_state *css)
  *
  * This is the blkcg counterpart of ioc_release_fn().
  */
-void blkcg_destroy_blkgs(struct blkcg *blkcg)
+static void blkcg_destroy_blkgs(struct blkcg *blkcg)
 {
 	might_sleep();
 
@@ -1075,6 +1067,57 @@ void blkcg_destroy_blkgs(struct blkcg *blkcg)
 	spin_unlock_irq(&blkcg->lock);
 }
 
+/**
+ * blkcg_pin_online - pin online state
+ * @blkcg_css: blkcg of interest
+ *
+ * While pinned, a blkcg is kept online.  This is primarily used to
+ * impedance-match blkg and cgwb lifetimes so that blkg doesn't go offline
+ * while an associated cgwb is still active.
+ */
+void blkcg_pin_online(struct cgroup_subsys_state *blkcg_css)
+{
+	refcount_inc(&css_to_blkcg(blkcg_css)->online_pin);
+}
+
+/**
+ * blkcg_unpin_online - unpin online state
+ * @blkcg_css: blkcg of interest
+ *
+ * This is primarily used to impedance-match blkg and cgwb lifetimes so
+ * that blkg doesn't go offline while an associated cgwb is still active.
+ * When this count goes to zero, all active cgwbs have finished so the
+ * blkcg can continue destruction by calling blkcg_destroy_blkgs().
+ */
+void blkcg_unpin_online(struct cgroup_subsys_state *blkcg_css)
+{
+	struct blkcg *blkcg = css_to_blkcg(blkcg_css);
+
+	do {
+		if (!refcount_dec_and_test(&blkcg->online_pin))
+			break;
+		blkcg_destroy_blkgs(blkcg);
+		blkcg = blkcg_parent(blkcg);
+	} while (blkcg);
+}
+
+/**
+ * blkcg_css_offline - cgroup css_offline callback
+ * @css: css of interest
+ *
+ * This function is called when @css is about to go away.  Here the cgwbs are
+ * offlined first and only once writeback associated with the blkcg has
+ * finished do we start step 2 (see above).
+ */
+static void blkcg_css_offline(struct cgroup_subsys_state *css)
+{
+	/* this prevents anyone from attaching or migrating to this blkcg */
+	wb_blkcg_offline(css_to_blkcg(css));
+
+	/* put the base online pin allowing step 2 to be triggered */
+	blkcg_unpin_online(css);
+}
+
 static void blkcg_css_free(struct cgroup_subsys_state *css)
 {
 	struct blkcg *blkcg = css_to_blkcg(css);
@@ -1163,8 +1206,7 @@ unlock:
 
 static int blkcg_css_online(struct cgroup_subsys_state *css)
 {
-	struct blkcg *blkcg = css_to_blkcg(css);
-	struct blkcg *parent = blkcg_parent(blkcg);
+	struct blkcg *parent = blkcg_parent(css_to_blkcg(css));
 
 	/*
 	 * blkcg_pin_online() is used to delay blkcg offline so that blkgs
@@ -1172,7 +1214,7 @@ static int blkcg_css_online(struct cgroup_subsys_state *css)
 	 * parent so that offline always happens towards the root.
 	 */
 	if (parent)
-		blkcg_pin_online(parent);
+		blkcg_pin_online(css);
 	return 0;
 }