cgroup: check cgroup liveliness before unbreaking kernfs
authorLi Zefan <lizefan@huawei.com>
Thu, 4 Sep 2014 06:43:38 +0000 (14:43 +0800)
committerTejun Heo <tj@kernel.org>
Thu, 4 Sep 2014 16:36:19 +0000 (01:36 +0900)
commitaa32362f011c6e863132b16c1761487166a4bad2
tree21274b6b6111e83af93568c4e7c10357f4e58a0f
parenta4189487da1b4f8260c6006b9dc47c3c4107a5ae
cgroup: check cgroup liveliness before unbreaking kernfs

When cgroup_kn_lock_live() is called through some kernfs operation and
another thread is calling cgroup_rmdir(), we'll trigger the warning in
cgroup_get().

------------[ cut here ]------------
WARNING: CPU: 1 PID: 1228 at kernel/cgroup.c:1034 cgroup_get+0x89/0xa0()
...
Call Trace:
 [<c16ee73d>] dump_stack+0x41/0x52
 [<c10468ef>] warn_slowpath_common+0x7f/0xa0
 [<c104692d>] warn_slowpath_null+0x1d/0x20
 [<c10bb999>] cgroup_get+0x89/0xa0
 [<c10bbe58>] cgroup_kn_lock_live+0x28/0x70
 [<c10be3c1>] __cgroup_procs_write.isra.26+0x51/0x230
 [<c10be5b2>] cgroup_tasks_write+0x12/0x20
 [<c10bb7b0>] cgroup_file_write+0x40/0x130
 [<c11aee71>] kernfs_fop_write+0xd1/0x160
 [<c1148e58>] vfs_write+0x98/0x1e0
 [<c114934d>] SyS_write+0x4d/0xa0
 [<c16f656b>] sysenter_do_call+0x12/0x12
---[ end trace 6f2e0c38c2108a74 ]---

Fix this by calling css_tryget() instead of cgroup_get().

v2:
- move cgroup_tryget() right below cgroup_get() definition. (Tejun)

Cc: <stable@vger.kernel.org> # 3.15+
Reported-by: Toralf Förster <toralf.foerster@gmx.de>
Signed-off-by: Zefan Li <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
kernel/cgroup.c