cgroups: remove events before destroying subsystem state objects

Events should be removed after rmdir of cgroup directory, but before
destroying subsystem state objects.  Let's take reference to cgroup
directory dentry to do that.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hioryu@jp.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Dan Malek <dan@embeddedalley.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 87441fc75663..ef909a329750 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2994,6 +2994,7 @@ static void cgroup_event_remove(struct work_struct *work)
 
         eventfd_ctx_put(event->eventfd);
         kfree(event);
+        dput(cgrp->dentry);
 }
 
 /*
@@ -3114,6 +3115,13 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
                 goto fail;
         }
 
+        /*
+         * Events should be removed after rmdir of cgroup directory, but before
+         * destroying subsystem state objects. Let's take reference to cgroup
+         * directory dentry to do that.
+         */
+        dget(cgrp->dentry);
+
         spin_lock(&cgrp->event_list_lock);
         list_add(&event->list, &cgrp->event_list);
         spin_unlock(&cgrp->event_list_lock);