Messages in this thread Patch in this message | | | Date | Thu, 15 Jan 2009 11:57:54 -0800 | From | Greg KH <> | Subject | [patch 19/94] cgroups: fix a race between cgroup_clone and umount |
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2.6.28-stable review patch. If anyone has any objections, please let us know.
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From: Li Zefan <lizf@cn.fujitsu.com>
commit 7b574b7b0124ed344911f5d581e9bc2d83bbeb19 upstream.
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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/cgroup.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
--- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2942,7 +2942,11 @@ int cgroup_clone(struct task_struct *tsk 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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