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);