Messages in this thread Patch in this message |  | | Date | Thu, 13 Feb 2014 13:29:31 -0500 | From | Tejun Heo <> | Subject | [PATCH cgroup/for-3.14-fixes] cgroup: update cgroup_enable_task_cg_lists() to grab siglock |
| |
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 <tj@kernel.org> Cc: stable@vger.kernel.org --- kernel/cgroup.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 68d8710..105f273 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2905,9 +2905,14 @@ static void cgroup_enable_task_cg_lists(void) * 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);
|  |