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Subject: Re: [RFC PATCH 1/2] mm, oom: marks all killed tasks as oom victims
To:     Michal Hocko <mhocko@kernel.org>
Cc:     linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>,
        David Rientjes <rientjes@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <20181022071323.9550-1-mhocko@kernel.org>
 <20181022071323.9550-2-mhocko@kernel.org>
 <201810220758.w9M7wojE016890@www262.sakura.ne.jp>
 <20181022084842.GW18839@dhcp22.suse.cz>
From:   Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Message-ID: <f5b257f9-47a5-e071-02fa-ce901bd34b04@i-love.sakura.ne.jp>
Date:   Mon, 22 Oct 2018 18:42:30 +0900
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On 2018/10/22 17:48, Michal Hocko wrote:
> On Mon 22-10-18 16:58:50, Tetsuo Handa wrote:
>> Michal Hocko wrote:
>>> --- a/mm/oom_kill.c
>>> +++ b/mm/oom_kill.c
>>> @@ -898,6 +898,7 @@ static void __oom_kill_process(struct task_struct *victim)
>>>  		if (unlikely(p->flags & PF_KTHREAD))
>>>  			continue;
>>>  		do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, PIDTYPE_TGID);
>>> +		mark_oom_victim(p);
>>>  	}
>>>  	rcu_read_unlock();
>>>  
>>> -- 
>>
>> Wrong. Either
> 
> You are right. The mm might go away between process_shares_mm and here.
> While your find_lock_task_mm would be correct I believe we can do better
> by using the existing mm that we already have. I will make it a separate
> patch to clarity.

Still wrong. p->mm == NULL means that we are too late to set TIF_MEMDIE
on that thread. Passing non-NULL mm to mark_oom_victim() won't help.

> @@ -898,7 +897,7 @@ static void __oom_kill_process(struct task_struct *victim)
>  		if (unlikely(p->flags & PF_KTHREAD))
>  			continue;
>  		do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, PIDTYPE_TGID);
> -		mark_oom_victim(p);
> +		mark_oom_victim(p, mm);
>  	}
>  	rcu_read_unlock();
>