From a320419451b152ce343bd59675a5bfa0beffe9e9 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 13 Feb 2014 13:29:31 -0500 Subject: [PATCH] cgroup: update cgroup_enable_task_cg_lists() to grab siglock 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 Acked-by: Li Zefan [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- kernel/cgroup.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 2a1ffb7b1915..93fc15e6ddcb 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2785,9 +2785,14 @@ 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, &p->cgroups->tasks); + spin_unlock_irq(&p->sighand->siglock); + task_unlock(p); } while_each_thread(g, p); write_unlock(&css_set_lock); -- 2.39.2