From 8e5bfa8c1f8471aa4a2d30be631ef2b50e10abaf Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 14 Nov 2016 19:46:12 +0100 Subject: sched/autogroup: Do not use autogroup->tg in zombie threads Exactly because for_each_thread() in autogroup_move_group() can't see it and update its ->sched_task_group before _put() and possibly free(). So the exiting task needs another sched_move_task() before exit_notify() and we need to re-introduce the PF_EXITING (or similar) check removed by the previous change for another reason. Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: hartsjc@redhat.com Cc: vbendel@redhat.com Cc: vlovejoy@redhat.com Link: http://lkml.kernel.org/r/20161114184612.GA15968@redhat.com Signed-off-by: Ingo Molnar --- kernel/exit.c | 1 + kernel/sched/auto_group.c | 19 +++++++++++++++++++ 2 files changed, 20 insertions(+) (limited to 'kernel') diff --git a/kernel/exit.c b/kernel/exit.c index 9d68c45ebbe3..3076f3089919 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -836,6 +836,7 @@ void __noreturn do_exit(long code) */ perf_event_exit_task(tsk); + sched_autogroup_exit_task(tsk); cgroup_exit(tsk); /* diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c index ad2b19ad6ca0..f1c8fd566246 100644 --- a/kernel/sched/auto_group.c +++ b/kernel/sched/auto_group.c @@ -115,10 +115,26 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg) * If we race with autogroup_move_group() the caller can use the old * value of signal->autogroup but in this case sched_move_task() will * be called again before autogroup_kref_put(). + * + * However, there is no way sched_autogroup_exit_task() could tell us + * to avoid autogroup->tg, so we abuse PF_EXITING flag for this case. */ + if (p->flags & PF_EXITING) + return false; + return true; } +void sched_autogroup_exit_task(struct task_struct *p) +{ + /* + * We are going to call exit_notify() and autogroup_move_group() can't + * see this thread after that: we can no longer use signal->autogroup. + * See the PF_EXITING check in task_wants_autogroup(). + */ + sched_move_task(p); +} + static void autogroup_move_group(struct task_struct *p, struct autogroup *ag) { @@ -142,6 +158,9 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag) * In the latter case for_each_thread() can not miss a migrating thread, * cpu_cgroup_attach() must not be possible after cgroup_exit() and it * can't be removed from thread list, we hold ->siglock. + * + * If an exiting thread was already removed from thread list we rely on + * sched_autogroup_exit_task(). */ for_each_thread(p, t) sched_move_task(t); -- cgit