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:	Fri, 15 Jul 2016 09:58:58 -0700
From:	Shayan Pooya <shayan@...eve.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Michal Hocko <mhocko@...nel.org>,
	Konstantin Khlebnikov <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

>> I am just curious... can you reproduce the problem reliably? If yes, can you try
>> the patch below ? Just in case, this is not the real fix in any case...
>
> Yes. It deterministically results in hung processes in vanilla kernel.
> I'll try this patch.

I'll have to correct this. I can reproduce this issue easily on
high-end servers and normal laptops. But for some reason it does not
happen very often in vmware guests (maybe related to lower
parallelism).

>> --- x/kernel/sched/core.c
>> +++ x/kernel/sched/core.c
>> @@ -2793,8 +2793,11 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
>>         balance_callback(rq);
>>         preempt_enable();
>>
>> -       if (current->set_child_tid)
>> +       if (current->set_child_tid) {
>> +               mem_cgroup_oom_enable();
>>                 put_user(task_pid_vnr(current), current->set_child_tid);
>> +               mem_cgroup_oom_disable();
>> +       }
>>  }
>>
>>  /*

I tried this patch and I still see the same stuck processes (assuming
that's what you were curious about).