From 532de3fc72adc2a6525c4d53c07bf81e1732083d Mon Sep 17 00:00:00 2001 From: Tejun Heo <tj@kernel.org> Date: Thu, 13 Feb 2014 13:29:31 -0500 Subject: [PATCH] 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> Acked-by: Li Zefan <lizefan@huawei.com> 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 68d87103b493a3..105f273b6f86a7 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); -- GitLab