linux-kernel - Re: [patch v3] mm, oom: fix unnecessary killing of additional processes

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Date:   Sat, 21 Jul 2018 05:47:30 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [patch v3] mm, oom: fix unnecessary killing of additional
 processes

On 2018/07/21 5:19, David Rientjes wrote:
> On Fri, 20 Jul 2018, Tetsuo Handa wrote:
> 
>>> Absent oom_lock serialization, this is exactly working as intended.  You 
>>> could argue that once the thread has reached exit_mmap() and begins oom 
>>> reaping that it should be allowed to finish before the oom reaper declares 
>>> MMF_OOM_SKIP.  That could certainly be helpful, I simply haven't 
>>> encountered a usecase where it were needed.  Or, we could restart the oom 
>>> expiration when MMF_UNSTABLE is set and deem that progress is being made 
>>> so it give it some extra time.  In practice, again, we haven't seen this 
>>> needed.  But either of those are very easy to add in as well.  Which would 
>>> you prefer?
>>
>> I don't think we need to introduce user-visible knob interface (even if it is in
>> debugfs), for I think that my approach can solve your problem. Please try OOM lockup
>> (CVE-2016-10723) mitigation patch ( https://marc.info/?l=linux-mm&m=153112243424285&w=4 )
> 
> The issue I am fixing has nothing to do with contention on oom_lock, it 
> has to do with the inability of the oom reaper to free memory for one or 
> more of several reasons: mlock, blockable mmus, ptes, mm->mmap_sem 
> contention, and then the setting of MMF_OOM_SKIP to choose another victim 
> before the original victim even reaches exit_mmap().  Thus, removing 
> oom_lock from exit_mmap() will not fix this issue.
> 
> I agree that oom_lock can be removed from exit_mmap() and it would be 
> helpful to do so, and may address a series of problems that we have yet to 
> encounter, but this would not fix the almost immediate setting of 
> MMF_OOM_SKIP that occurs with minimal memory freeing due to the oom 
> reaper.
> 

Why [PATCH 2/2] in https://marc.info/?l=linux-mm&m=153119509215026&w=4 does not
solve your problem?