blkcg: kill blkio_list and replace blkio_list_lock with a mutex

With blkio_policy[], blkio_list is redundant and hinders with
per-queue policy activation.  Remove it.  Also, replace
blkio_list_lock with a mutex blkcg_pol_mutex and let it protect the
whole [un]registration.

This is to prepare for per-queue policy activation and doesn't cause
any functional difference.

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

2 files changed, 17 insertions, 16 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 9449c383b7ba..af665fe7f4f2 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -24,9 +24,7 @@
 
 #define MAX_KEY_LEN 100
 
-static DEFINE_SPINLOCK(blkio_list_lock);
-static LIST_HEAD(blkio_list);
-
+static DEFINE_MUTEX(blkcg_pol_mutex);
 static DEFINE_MUTEX(all_q_mutex);
 static LIST_HEAD(all_q_list);
 
@@ -311,8 +309,9 @@ blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
         struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
         struct blkio_group *blkg;
         struct hlist_node *n;
+        int i;
 
-        spin_lock(&blkio_list_lock);
+        mutex_lock(&blkcg_pol_mutex);
         spin_lock_irq(&blkcg->lock);
 
         /*
@@ -321,15 +320,16 @@ blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
          * anyway.  If you get hit by a race, retry.
          */
         hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
-                struct blkio_policy_type *pol;
+                for (i = 0; i < BLKIO_NR_POLICIES; i++) {
+                        struct blkio_policy_type *pol = blkio_policy[i];
 
-                list_for_each_entry(pol, &blkio_list, list)
-                        if (pol->ops.blkio_reset_group_stats_fn)
+                        if (pol && pol->ops.blkio_reset_group_stats_fn)
                                 pol->ops.blkio_reset_group_stats_fn(blkg);
+                }
         }
 
         spin_unlock_irq(&blkcg->lock);
-        spin_unlock(&blkio_list_lock);
+        mutex_unlock(&blkcg_pol_mutex);
         return 0;
 }
 
@@ -732,20 +732,21 @@ void blkio_policy_register(struct blkio_policy_type *blkiop)
 {
         struct request_queue *q;
 
+        mutex_lock(&blkcg_pol_mutex);
+
         blkcg_bypass_start();
-        spin_lock(&blkio_list_lock);
 
         BUG_ON(blkio_policy[blkiop->plid]);
         blkio_policy[blkiop->plid] = blkiop;
-        list_add_tail(&blkiop->list, &blkio_list);
-
-        spin_unlock(&blkio_list_lock);
         list_for_each_entry(q, &all_q_list, all_q_node)
                 update_root_blkg_pd(q, blkiop->plid);
+
         blkcg_bypass_end();
 
         if (blkiop->cftypes)
                 WARN_ON(cgroup_add_cftypes(&blkio_subsys, blkiop->cftypes));
+
+        mutex_unlock(&blkcg_pol_mutex);
 }
 EXPORT_SYMBOL_GPL(blkio_policy_register);
 
@@ -753,19 +754,20 @@ void blkio_policy_unregister(struct blkio_policy_type *blkiop)
 {
         struct request_queue *q;
 
+        mutex_lock(&blkcg_pol_mutex);
+
         if (blkiop->cftypes)
                 cgroup_rm_cftypes(&blkio_subsys, blkiop->cftypes);
 
         blkcg_bypass_start();
-        spin_lock(&blkio_list_lock);
 
         BUG_ON(blkio_policy[blkiop->plid] != blkiop);
         blkio_policy[blkiop->plid] = NULL;
-        list_del_init(&blkiop->list);
 
-        spin_unlock(&blkio_list_lock);
         list_for_each_entry(q, &all_q_list, all_q_node)
                 update_root_blkg_pd(q, blkiop->plid);
         blkcg_bypass_end();
+
+        mutex_unlock(&blkcg_pol_mutex);
 }
 EXPORT_SYMBOL_GPL(blkio_policy_unregister);
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 64392ac76ce8..c772581c9011 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -102,7 +102,6 @@ struct blkio_policy_ops {
 };
 
 struct blkio_policy_type {
-        struct list_head list;
         struct blkio_policy_ops ops;
         enum blkio_policy_id plid;
         size_t pdata_size;              /* policy specific private data size */