blkcg: implement blkcg_policy->on/offline_pd_fn() and blkcg_gq->online

Add two blkcg_policy methods, ->online_pd_fn() and ->offline_pd_fn(),
which are invoked as the policy_data gets activated and deactivated
while holding both blkcg and q locks.

Also, add blkcg_gq->online bool, which is set and cleared as the
blkcg_gq gets activated and deactivated.  This flag also is toggled
while holding both blkcg and q locks.

These will be used to implement hierarchical stats.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>

2 files changed, 27 insertions, 1 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 3a8de321d1f6..4d625d28e070 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -182,7 +182,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
                                     struct blkcg_gq *new_blkg)
 {
         struct blkcg_gq *blkg;
-        int ret;
+        int i, ret;
 
         WARN_ON_ONCE(!rcu_read_lock_held());
         lockdep_assert_held(q->queue_lock);
@@ -218,7 +218,15 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
         if (likely(!ret)) {
                 hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
                 list_add(&blkg->q_node, &q->blkg_list);
+
+                for (i = 0; i < BLKCG_MAX_POLS; i++) {
+                        struct blkcg_policy *pol = blkcg_policy[i];
+
+                        if (blkg->pd[i] && pol->pd_online_fn)
+                                pol->pd_online_fn(blkg);
+                }
         }
+        blkg->online = true;
         spin_unlock(&blkcg->lock);
 
         if (!ret)
@@ -291,6 +299,7 @@ EXPORT_SYMBOL_GPL(blkg_lookup_create);
 static void blkg_destroy(struct blkcg_gq *blkg)
 {
         struct blkcg *blkcg = blkg->blkcg;
+        int i;
 
         lockdep_assert_held(blkg->q->queue_lock);
         lockdep_assert_held(&blkcg->lock);
@@ -299,6 +308,14 @@ static void blkg_destroy(struct blkcg_gq *blkg)
         WARN_ON_ONCE(list_empty(&blkg->q_node));
         WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
 
+        for (i = 0; i < BLKCG_MAX_POLS; i++) {
+                struct blkcg_policy *pol = blkcg_policy[i];
+
+                if (blkg->pd[i] && pol->pd_offline_fn)
+                        pol->pd_offline_fn(blkg);
+        }
+        blkg->online = false;
+
         radix_tree_delete(&blkcg->blkg_tree, blkg->q->id);
         list_del_init(&blkg->q_node);
         hlist_del_init_rcu(&blkg->blkcg_node);
@@ -956,6 +973,8 @@ void blkcg_deactivate_policy(struct request_queue *q,
                 /* grab blkcg lock too while removing @pd from @blkg */
                 spin_lock(&blkg->blkcg->lock);
 
+                if (pol->pd_offline_fn)
+                        pol->pd_offline_fn(blkg);
                 if (pol->pd_exit_fn)
                         pol->pd_exit_fn(blkg);
 
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 40f5b9768aac..678e89ed8ecb 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -106,12 +106,17 @@ struct blkcg_gq {
         /* reference count */
         int                             refcnt;
 
+        /* is this blkg online? protected by both blkcg and q locks */
+        bool                            online;
+
         struct blkg_policy_data         *pd[BLKCG_MAX_POLS];
 
         struct rcu_head                 rcu_head;
 };
 
 typedef void (blkcg_pol_init_pd_fn)(struct blkcg_gq *blkg);
+typedef void (blkcg_pol_online_pd_fn)(struct blkcg_gq *blkg);
+typedef void (blkcg_pol_offline_pd_fn)(struct blkcg_gq *blkg);
 typedef void (blkcg_pol_exit_pd_fn)(struct blkcg_gq *blkg);
 typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkcg_gq *blkg);
 
@@ -124,6 +129,8 @@ struct blkcg_policy {
 
         /* operations */
         blkcg_pol_init_pd_fn            *pd_init_fn;
+        blkcg_pol_online_pd_fn          *pd_online_fn;
+        blkcg_pol_offline_pd_fn         *pd_offline_fn;
         blkcg_pol_exit_pd_fn            *pd_exit_fn;
         blkcg_pol_reset_pd_stats_fn     *pd_reset_stats_fn;
 };