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, 4 insertions, 54 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 9c8a12477e13..153ba509446b 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -54,7 +54,6 @@ struct throtl_grp {
          */
         unsigned long disptime;
 
-        atomic_t ref;
         unsigned int flags;
 
         /* Two lists for READ and WRITE */
@@ -80,8 +79,6 @@ struct throtl_grp {
 
         /* Some throttle limits got updated for the group */
         int limits_changed;
-
-        struct rcu_head rcu_head;
 };
 
 struct throtl_data
@@ -151,45 +148,6 @@ static inline unsigned int total_nr_queued(struct throtl_data *td)
         return td->nr_queued[0] + td->nr_queued[1];
 }
 
-static inline struct throtl_grp *throtl_ref_get_tg(struct throtl_grp *tg)
-{
-        atomic_inc(&tg->ref);
-        return tg;
-}
-
-static void throtl_free_tg(struct rcu_head *head)
-{
-        struct throtl_grp *tg = container_of(head, struct throtl_grp, rcu_head);
-        struct blkio_group *blkg = tg_to_blkg(tg);
-
-        free_percpu(blkg->stats_cpu);
-        kfree(blkg->pd);
-        kfree(blkg);
-}
-
-static void throtl_put_tg(struct throtl_grp *tg)
-{
-        struct blkio_group *blkg = tg_to_blkg(tg);
-
-        BUG_ON(atomic_read(&tg->ref) <= 0);
-        if (!atomic_dec_and_test(&tg->ref))
-                return;
-
-        /* release the extra blkcg reference this blkg has been holding */
-        css_put(&blkg->blkcg->css);
-
-        /*
-         * A group is freed in rcu manner. But having an rcu lock does not
-         * mean that one can access all the fields of blkg and assume these
-         * are valid. For example, don't try to follow throtl_data and
-         * request queue links.
-         *
-         * Having a reference to blkg under an rcu allows acess to only
-         * values local to groups like group stats and group rate limits
-         */
-        call_rcu(&tg->rcu_head, throtl_free_tg);
-}
-
 static void throtl_init_blkio_group(struct blkio_group *blkg)
 {
         struct throtl_grp *tg = blkg_to_tg(blkg);
@@ -204,14 +162,6 @@ static void throtl_init_blkio_group(struct blkio_group *blkg)
         tg->bps[WRITE] = -1;
         tg->iops[READ] = -1;
         tg->iops[WRITE] = -1;
-
-        /*
-         * Take the initial reference that will be released on destroy
-         * This can be thought of a joint reference by cgroup and
-         * request queue which will be dropped by either request queue
-         * exit or cgroup deletion path depending on who is exiting first.
-         */
-        atomic_set(&tg->ref, 1);
 }
 
 static void throtl_link_blkio_group(struct request_queue *q,
@@ -648,7 +598,7 @@ static void throtl_add_bio_tg(struct throtl_data *td, struct throtl_grp *tg,
 
         bio_list_add(&tg->bio_lists[rw], bio);
         /* Take a bio reference on tg */
-        throtl_ref_get_tg(tg);
+        blkg_get(tg_to_blkg(tg));
         tg->nr_queued[rw]++;
         td->nr_queued[rw]++;
         throtl_enqueue_tg(td, tg);
@@ -681,8 +631,8 @@ static void tg_dispatch_one_bio(struct throtl_data *td, struct throtl_grp *tg,
 
         bio = bio_list_pop(&tg->bio_lists[rw]);
         tg->nr_queued[rw]--;
-        /* Drop bio reference on tg */
-        throtl_put_tg(tg);
+        /* Drop bio reference on blkg */
+        blkg_put(tg_to_blkg(tg));
 
         BUG_ON(td->nr_queued[rw] <= 0);
         td->nr_queued[rw]--;
@@ -880,7 +830,7 @@ throtl_destroy_tg(struct throtl_data *td, struct throtl_grp *tg)
          * Put the reference taken at the time of creation so that when all
          * queues are gone, group can be destroyed.
          */
-        throtl_put_tg(tg);
+        blkg_put(tg_to_blkg(tg));
         td->nr_undestroyed_grps--;
 }