cgroup: no need to check css refs for release notification
authorLi Zefan <lizefan@huawei.com>
Fri, 1 Mar 2013 07:06:07 +0000 (15:06 +0800)
committerTejun Heo <tj@kernel.org>
Mon, 4 Mar 2013 18:04:54 +0000 (10:04 -0800)
commitf50daa704f36a6544a902c52b6cf37b0493dfc5d
tree157d40fe53c6cde3aa2c2644b35dbe687e547dcc
parentf440d98f8ebab02a768c1de17395e4239af9a97d
cgroup: no need to check css refs for release notification

We no longer fail rmdir() when there're still css refs, so we don't
need to check css refs in check_for_release().

This also voids a bug. cgroup_has_css_refs() accesses subsys[i]
without cgroup_mutex, so it can race with cgroup_unload_subsys().

cgroup_has_css_refs()
...
  if (ss == NULL || ss->root != cgrp->root)

if ss pointers to net_cls_subsys, and cls_cgroup module is unloaded
right after the former check but before the latter, the memory that
net_cls_subsys resides has become invalid.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
kernel/cgroup.c