blkcg: move refcnt to blkcg core

Currently, blkcg policy implementations manage blkg refcnt duplicating
mostly identical code in both policies.  This patch moves refcnt to
blkg and let blkcg core handle refcnt and freeing of blkgs.

* cfq blkgs now also get freed via RCU.

* cfq blkgs lose RB_EMPTY_ROOT() sanity check on blkg free.  If
  necessary, we can add blkio_exit_group_fn() to resurrect this.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 35 insertions, 0 deletions

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 9537819c29c6..7da106843f01 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -177,6 +177,8 @@ struct blkio_group {
         char path[128];
         /* policy which owns this blk group */
         enum blkio_policy_id plid;
+        /* reference count */
+        int refcnt;
 
         /* Configuration */
         struct blkio_group_conf conf;
@@ -188,6 +190,8 @@ struct blkio_group {
         struct blkio_group_stats_cpu __percpu *stats_cpu;
 
         struct blkg_policy_data *pd;
+
+        struct rcu_head rcu_head;
 };
 
 typedef void (blkio_init_group_fn)(struct blkio_group *blkg);
@@ -272,6 +276,35 @@ static inline char *blkg_path(struct blkio_group *blkg)
         return blkg->path;
 }
 
+/**
+ * blkg_get - get a blkg reference
+ * @blkg: blkg to get
+ *
+ * The caller should be holding queue_lock and an existing reference.
+ */
+static inline void blkg_get(struct blkio_group *blkg)
+{
+        lockdep_assert_held(blkg->q->queue_lock);
+        WARN_ON_ONCE(!blkg->refcnt);
+        blkg->refcnt++;
+}
+
+void __blkg_release(struct blkio_group *blkg);
+
+/**
+ * blkg_put - put a blkg reference
+ * @blkg: blkg to put
+ *
+ * The caller should be holding queue_lock.
+ */
+static inline void blkg_put(struct blkio_group *blkg)
+{
+        lockdep_assert_held(blkg->q->queue_lock);
+        WARN_ON_ONCE(blkg->refcnt <= 0);
+        if (!--blkg->refcnt)
+                __blkg_release(blkg);
+}
+
 #else
 
 struct blkio_group {
@@ -292,6 +325,8 @@ static inline void *blkg_to_pdata(struct blkio_group *blkg,
 static inline struct blkio_group *pdata_to_blkg(void *pdata,
                                 struct blkio_policy_type *pol) { return NULL; }
 static inline char *blkg_path(struct blkio_group *blkg) { return NULL; }
+static inline void blkg_get(struct blkio_group *blkg) { }
+static inline void blkg_put(struct blkio_group *blkg) { }
 
 #endif