Messages in this thread | | | Subject | Re: sched/autogroup: race if !sysctl_sched_autogroup_enabled ? | From | Mike Galbraith <> | Date | Sat, 12 Nov 2016 13:12:29 +0100 |
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On Wed, 2016-11-09 at 18:50 +0100, Peter Zijlstra wrote: > On Wed, Nov 09, 2016 at 05:59:33PM +0100, Oleg Nesterov wrote: > > > We need to ensure that autogroup/tg returned by autogroup_task_group() > > can't go away if we race with autogroup_move_group(), and unless the > > caller holds ->siglock we rely on fact that autogroup_move_group() > > will a) see this task and b) do sched_move_task() which needs the same > > same rq->lock. > > > > However. autogroup_move_group() skips for_each_thread/sched_move_task > > if sysctl_sched_autogroup_enabled == 0. > > > > So. Doesn't this mean that cgroup migration to the root cgroup can race > > with autogroup_move_group() and use the soon-to-be-freed autogroup->tg? > > Argh, its too late for this, also jet-lag. But maybe, I can sort of feel > a hole here but cannot for the life of me still think. > > > > although this is a bit off-topic. Another question is that I fail to > > understand why sched_autogroup_create_attach() does autogroup_create() > > and changes signal->autogroup even if !sysctl_sched_autogroup_enabled. > > I really cannot remember back that far, but it could be to allow > flipping it back on. Then again, I don't think the fork path puts new > tasks in, even if the autogroup exists.
Yeah, I've forgotten nearly everything about it too. I do recall that the autogroup always existed for both manual on/off and migrations cgroup <--> root.
I think autogroup should go away. Systemthing infestation is nearly everywhere these days, and it wants to do ever more stupid shite that will render it useless anyway.
-Mike
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