From 7b574b7b0124ed344911f5d581e9bc2d83bbeb19 Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Sun, 4 Jan 2009 12:00:45 -0800 Subject: [PATCH] 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: [] ? deactivate_super+0x3f/0x51 [] ? mntput_no_expire+0xb3/0xdd [] ? sys_umount+0x265/0x2ac [] ? sys_oldumount+0xd/0xf [] ? sysenter_do_call+0x12/0x31 ... EIP: [] cgroup_kill_sb+0x23/0xe0 SS:ESP 0068:e411ef2c ---[ end trace c766c1be3bf944ac ]--- Cc: Serge E. Hallyn Signed-off-by: Li Zefan Cc: Paul Menage Cc: "Serge E. Hallyn" Cc: Balbir Singh Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/cgroup.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 48348dde6d81..891a84eb9d30 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -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); -- 2.20.1