Commit 7b574b7b authored Jan 04, 2009 by Li Zefan Committed by Linus Torvalds Jan 04, 2009

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 <serue@us.ibm.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: "Serge E. Hallyn" <serue@us.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 7d3b56ba

kernel/cgroup.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -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 */
		atomic_inc(&parent->root->sb->s_active);
		if (!atomic_inc_not_zero(&parent->root->sb->s_active)) {
		/* We race with the final deactivate_super() */
		mutex_unlock(&cgroup_mutex);
		return 0;
		}

		/* Keep the cgroup alive */
		get_css_set(cg);

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