3.13-stable review patch. If anyone has any objections, please let me know.
------------------
From: Tejun Heo <t...@kernel.org>
commit 532de3fc72adc2a6525c4d53c07bf81e1732083d upstream.
Currently, there's nothing preventing cgroup_enable_task_cg_lists()
from missing set PF_EXITING and race against cgroup_exit(). Depending
on the timing, cgroup_exit() may finish with the task still linked on
css_set leading to list corruption. Fix it by grabbing siglock in
cgroup_enable_task_cg_lists() so that PF_EXITING is guaranteed to be
visible.
This whole on-demand cg_list optimization is extremely fragile and has
ample possibility to lead to bugs which can cause things like
once-a-year oops during boot. I'm wondering whether the better
approach would be just adding "cgroup_disable=all" handling which
disables the whole cgroup rather than tempting fate with this
on-demand craziness.
Signed-off-by: Tejun Heo <t...@kernel.org>
Acked-by: Li Zefan <lize...@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
kernel/cgroup.c | 5 +++++
1 file changed, 5 insertions(+)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2985,9 +2985,14 @@ static void cgroup_enable_task_cg_lists(
* We should check if the process is exiting, otherwise
* it will race with cgroup_exit() in that the list
* entry won't be deleted though the process has exited.
+ * Do it while holding siglock so that we don't end up
+ * racing against cgroup_exit().
*/
+ spin_lock_irq(&p->sighand->siglock);
if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
list_add(&p->cg_list, &task_css_set(p)->tasks);
+ spin_unlock_irq(&p->sighand->siglock);
+
task_unlock(p);
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
--
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