Commit 7b574b7b authored by Li Zefan's avatar Li Zefan Committed by Linus Torvalds
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cgroups: fix a race between cgroup_clone and umount

The race is calling cgroup_clone() while umounting the ns cgroup subsys,
and thus cgroup_clone() might access invalid cgroup_fs, or kill_sb() is
called after cgroup_clone() created a new dir in it.

The BUG I triggered is BUG_ON(root->number_of_cgroups != 1);

  ------------[ cut here ]------------
  kernel BUG at kernel/cgroup.c:1093!
  invalid opcode: 0000 [#1] SMP
  Process umount (pid: 5177, ti=e411e000 task=e40c4670 task.ti=e411e000)
  Call Trace:
   [<c0493df7>] ? deactivate_super+0x3f/0x51
   [<c04a3600>] ? mntput_no_expire+0xb3/0xdd
   [<c04a3ab2>] ? sys_umount+0x265/0x2ac
   [<c04a3b06>] ? sys_oldumount+0xd/0xf
   [<c0403911>] ? sysenter_do_call+0x12/0x31
  EIP: [<c0456e76>] cgroup_kill_sb+0x23/0xe0 SS:ESP 0068:e411ef2c
  ---[ end trace c766c1be3bf944ac ]---

Cc: Serge E. Hallyn <>
Signed-off-by: default avatarLi Zefan <>
Cc: Paul Menage <>
Cc: "Serge E. Hallyn" <>
Cc: Balbir Singh <>
Cc: <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 7d3b56ba
......@@ -2945,7 +2945,11 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
parent = task_cgroup(tsk, subsys->subsys_id);
/* Pin the hierarchy */
if (!atomic_inc_not_zero(&parent->root->sb->s_active)) {
/* We race with the final deactivate_super() */
return 0;
/* Keep the cgroup alive */
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