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authorLi Zefan <lizf@cn.fujitsu.com>2009-01-04 12:00:45 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-01-04 13:33:19 -0800
commit7b574b7b0124ed344911f5d581e9bc2d83bbeb19 (patch)
tree6511203310d77359017accb466f3f5e1e90abe13 /kernel
parent7d3b56ba37a95f1f370f50258ed3954c304c524b (diff)
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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 <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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cgroup.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 48348dde6d8..891a84eb9d3 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);