Merge branch 'for-3.13-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup fixes from Tejun Heo:
 "Two fixes.  One fixes a bug in the error path of cgroup_create().  The
  other changes cgrp->id lifetime rule so that the id doesn't get
  recycled before all controller states are destroyed.  This premature
  id recycling made memcg malfunction"

* 'for-3.13-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: don't recycle cgroup id until all csses' have been destroyed
  cgroup: fix cgroup_create() error handling path

1 files changed, 32 insertions, 18 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8b729c278b64..bc1dcabe9217 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -890,6 +890,16 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
                 struct cgroup *cgrp = dentry->d_fsdata;
 
                 BUG_ON(!(cgroup_is_dead(cgrp)));
+
+                /*
+                 * XXX: cgrp->id is only used to look up css's.  As cgroup
+                 * and css's lifetimes will be decoupled, it should be made
+                 * per-subsystem and moved to css->id so that lookups are
+                 * successful until the target css is released.
+                 */
+                idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
+                cgrp->id = -1;
+
                 call_rcu(&cgrp->rcu_head, cgroup_free_rcu);
         } else {
                 struct cfent *cfe = __d_cfe(dentry);
@@ -4268,6 +4278,7 @@ static void css_release(struct percpu_ref *ref)
         struct cgroup_subsys_state *css =
                 container_of(ref, struct cgroup_subsys_state, refcnt);
 
+        rcu_assign_pointer(css->cgroup->subsys[css->ss->subsys_id], NULL);
         call_rcu(&css->rcu_head, css_free_rcu_fn);
 }
 
@@ -4426,14 +4437,6 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
         list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children);
         root->number_of_cgroups++;
 
-        /* each css holds a ref to the cgroup's dentry and the parent css */
-        for_each_root_subsys(root, ss) {
-                struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
-
-                dget(dentry);
-                css_get(css->parent);
-        }
-
         /* hold a ref to the parent's dentry */
         dget(parent->dentry);
 
@@ -4445,6 +4448,13 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                 if (err)
                         goto err_destroy;
 
+                /* each css holds a ref to the cgroup's dentry and parent css */
+                dget(dentry);
+                css_get(css->parent);
+
+                /* mark it consumed for error path */
+                css_ar[ss->subsys_id] = NULL;
+
                 if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
                     parent->parent) {
                         pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
@@ -4491,6 +4501,14 @@ err_free_cgrp:
         return err;
 
 err_destroy:
+        for_each_root_subsys(root, ss) {
+                struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
+
+                if (css) {
+                        percpu_ref_cancel_init(&css->refcnt);
+                        ss->css_free(css);
+                }
+        }
         cgroup_destroy_locked(cgrp);
         mutex_unlock(&cgroup_mutex);
         mutex_unlock(&dentry->d_inode->i_mutex);
@@ -4652,8 +4670,12 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
          * will be invoked to perform the rest of destruction once the
          * percpu refs of all css's are confirmed to be killed.
          */
-        for_each_root_subsys(cgrp->root, ss)
-                kill_css(cgroup_css(cgrp, ss));
+        for_each_root_subsys(cgrp->root, ss) {
+                struct cgroup_subsys_state *css = cgroup_css(cgrp, ss);
+
+                if (css)
+                        kill_css(css);
+        }
 
         /*
          * Mark @cgrp dead.  This prevents further task migration and child
@@ -4722,14 +4744,6 @@ static void cgroup_destroy_css_killed(struct cgroup *cgrp)
         /* delete this cgroup from parent->children */
         list_del_rcu(&cgrp->sibling);
 
-        /*
-         * We should remove the cgroup object from idr before its grace
-         * period starts, so we won't be looking up a cgroup while the
-         * cgroup is being freed.
-         */
-        idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
-        cgrp->id = -1;
-
         dput(d);
 
         set_bit(CGRP_RELEASABLE, &parent->flags);