linux-kernel - Re: bug in memcg oom-killer results in a hung syscall in another process in the same cgroup

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Date:	Tue, 12 Jul 2016 18:52:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:	Shayan Pooya <shayan@...eve.org>, Michal Hocko <mhocko@...nel.org>,
	koct9i@...il.com, cgroups mailinglist <cgroups@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: bug in memcg oom-killer results in a hung syscall in another
	process in the same cgroup

On 07/12, Konstantin Khlebnikov wrote:
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2808,8 +2808,9 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
>         balance_callback(rq);
>         preempt_enable();
>
> -       if (current->set_child_tid)
> -               put_user(task_pid_vnr(current), current->set_child_tid);
> +       if (current->set_child_tid &&
> +           put_user(task_pid_vnr(current), current->set_child_tid))
> +               force_sig(SIGSEGV, current);
>  }
>
> Add Oleg into CC. IIRR he had some ideas how to fix this. =)

Heh. OK, OK, thank you Konstantin ;)

I'll try to recall tomorrow, but iirc I only have some ideas of how
we can happily blame the FAULT_FLAG_USER logic.

d, in this particular case, perhaps glibc/set_child_tid too because
(again, iirc) it would nice to simply kill it, it is only used for
some sanity checks...

Oleg.