blkio: Take care of cgroup deletion and cfq group reference counting

o One can choose to change elevator or delete a cgroup. Implement group
  reference counting so that both elevator exit and cgroup deletion can
  take place gracefully.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Nauman Rafique <nauman@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 64 insertions, 2 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 4f6afd76ec59..0426ab692fd5 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -13,6 +13,8 @@
 #include <linux/ioprio.h>
 #include "blk-cgroup.h"
 
+extern void cfq_unlink_blkio_group(void *, struct blkio_group *);
+
 struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT };
 
 struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup)
@@ -28,14 +30,43 @@ void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
 
         spin_lock_irqsave(&blkcg->lock, flags);
         rcu_assign_pointer(blkg->key, key);
+        blkg->blkcg_id = css_id(&blkcg->css);
         hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
         spin_unlock_irqrestore(&blkcg->lock, flags);
 }
 
+static void __blkiocg_del_blkio_group(struct blkio_group *blkg)
+{
+        hlist_del_init_rcu(&blkg->blkcg_node);
+        blkg->blkcg_id = 0;
+}
+
+/*
+ * returns 0 if blkio_group was still on cgroup list. Otherwise returns 1
+ * indicating that blk_group was unhashed by the time we got to it.
+ */
 int blkiocg_del_blkio_group(struct blkio_group *blkg)
 {
-        /* Implemented later */
-        return 0;
+        struct blkio_cgroup *blkcg;
+        unsigned long flags;
+        struct cgroup_subsys_state *css;
+        int ret = 1;
+
+        rcu_read_lock();
+        css = css_lookup(&blkio_subsys, blkg->blkcg_id);
+        if (!css)
+                goto out;
+
+        blkcg = container_of(css, struct blkio_cgroup, css);
+        spin_lock_irqsave(&blkcg->lock, flags);
+        if (!hlist_unhashed(&blkg->blkcg_node)) {
+                __blkiocg_del_blkio_group(blkg);
+                ret = 0;
+        }
+        spin_unlock_irqrestore(&blkcg->lock, flags);
+out:
+        rcu_read_unlock();
+        return ret;
 }
 
 /* called under rcu_read_lock(). */
@@ -97,8 +128,39 @@ static int blkiocg_populate(struct cgroup_subsys *subsys, struct cgroup *cgroup)
 static void blkiocg_destroy(struct cgroup_subsys *subsys, struct cgroup *cgroup)
 {
         struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
+        unsigned long flags;
+        struct blkio_group *blkg;
+        void *key;
 
+        rcu_read_lock();
+remove_entry:
+        spin_lock_irqsave(&blkcg->lock, flags);
+
+        if (hlist_empty(&blkcg->blkg_list)) {
+                spin_unlock_irqrestore(&blkcg->lock, flags);
+                goto done;
+        }
+
+        blkg = hlist_entry(blkcg->blkg_list.first, struct blkio_group,
+                                blkcg_node);
+        key = rcu_dereference(blkg->key);
+        __blkiocg_del_blkio_group(blkg);
+
+        spin_unlock_irqrestore(&blkcg->lock, flags);
+
+        /*
+         * This blkio_group is being unlinked as associated cgroup is going
+         * away. Let all the IO controlling policies know about this event.
+         *
+         * Currently this is static call to one io controlling policy. Once
+         * we have more policies in place, we need some dynamic registration
+         * of callback function.
+         */
+        cfq_unlink_blkio_group(key, blkg);
+        goto remove_entry;
+done:
         free_css_id(&blkio_subsys, &blkcg->css);
+        rcu_read_unlock();
         kfree(blkcg);
 }