Messages in this thread Patch in this message | | | Date | Thu, 25 Dec 2008 11:47:09 +0800 | From | Li Zefan <> | Subject | [PATCH] cgroups: fix a race between cgroup_clone and umount |
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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> ---
affected kernel: 2.6.24 to 2.6.28
--- kernel/cgroup.c | 6 +++++- 1 files changed, 5 insertions(+), 1 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 2606d0f..c882385 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2942,7 +2942,11 @@ 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); -- 1.5.4.rc3
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