• Li Zefan's avatar
    cgroup: check cgroup liveliness before unbreaking kernfs · aa32362f
    Li Zefan authored
    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: default avatarToralf Förster <toralf.foerster@gmx.de>
    Signed-off-by: default avatarZefan Li <lizefan@huawei.com>
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    aa32362f
cgroup.c 151 KB