blkcg: implement all_blkcgs list

Add all_blkcgs list goes through blkcg->all_blkcgs_node and is
protected by blkcg_pol_mutex.  This will be used to fix
blkcg_policy_data allocation bug.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

2 files changed, 13 insertions, 5 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 05b893de516b..42ff436ffaf4 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -46,6 +46,8 @@ struct cgroup_subsys_state * const blkcg_root_css = &blkcg_root.css;
 
 static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
 
+static LIST_HEAD(all_blkcgs);           /* protected by blkcg_pol_mutex */
+
 static bool blkcg_policy_enabled(struct request_queue *q,
                                  const struct blkcg_policy *pol)
 {
@@ -817,6 +819,10 @@ static void blkcg_css_free(struct cgroup_subsys_state *css)
 {
         struct blkcg *blkcg = css_to_blkcg(css);
 
+        mutex_lock(&blkcg_pol_mutex);
+        list_del(&blkcg->all_blkcgs_node);
+        mutex_unlock(&blkcg_pol_mutex);
+
         if (blkcg != &blkcg_root) {
                 int i;
 
@@ -833,6 +839,8 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
         struct cgroup_subsys_state *ret;
         int i;
 
+        mutex_lock(&blkcg_pol_mutex);
+
         if (!parent_css) {
                 blkcg = &blkcg_root;
                 goto done;
@@ -844,8 +852,6 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
                 goto free_blkcg;
         }
 
-        mutex_lock(&blkcg_pol_mutex);
-
         for (i = 0; i < BLKCG_MAX_POLS ; i++) {
                 struct blkcg_policy *pol = blkcg_policy[i];
                 struct blkcg_policy_data *cpd;
@@ -862,7 +868,6 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
                 BUG_ON(blkcg->pd[i]);
                 cpd = kzalloc(pol->cpd_size, GFP_KERNEL);
                 if (!cpd) {
-                        mutex_unlock(&blkcg_pol_mutex);
                         ret = ERR_PTR(-ENOMEM);
                         goto free_pd_blkcg;
                 }
@@ -871,7 +876,6 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
                 pol->cpd_init_fn(blkcg);
         }
 
-        mutex_unlock(&blkcg_pol_mutex);
 done:
         spin_lock_init(&blkcg->lock);
         INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_ATOMIC);
@@ -879,14 +883,17 @@ done:
 #ifdef CONFIG_CGROUP_WRITEBACK
         INIT_LIST_HEAD(&blkcg->cgwb_list);
 #endif
+        list_add_tail(&blkcg->all_blkcgs_node, &all_blkcgs);
+
+        mutex_unlock(&blkcg_pol_mutex);
         return &blkcg->css;
 
 free_pd_blkcg:
         for (i--; i >= 0; i--)
                 kfree(blkcg->pd[i]);
-
 free_blkcg:
         kfree(blkcg);
+        mutex_unlock(&blkcg_pol_mutex);
         return ret;
 }
 
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 58cfab80dd70..cf3e7bc22ef3 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -47,6 +47,7 @@ struct blkcg {
 
         struct blkcg_policy_data        *pd[BLKCG_MAX_POLS];
 
+        struct list_head                all_blkcgs_node;
 #ifdef CONFIG_CGROUP_WRITEBACK
         struct list_head                cgwb_list;
 #endif