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From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: mhocko@kernel.org
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
	wenwei.tww@alibaba-inc.com, oleg@redhat.com, rientjes@google.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm, oom: fix potential data corruption when oom_reaper races with writer
Date: Sat, 5 Aug 2017 01:49:17 +0900	[thread overview]
Message-ID: <201708050149.JEC09861.MOLFtQFFVJOSOH@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20170804145631.GP26029@dhcp22.suse.cz>

Michal Hocko wrote:
> And that's why we still see the corruption. That, however, means that
> the MMF_UNSTABLE implementation has to be more complex and we have to
> hook into all anonymous memory fault paths which I hoped I could avoid
> previously.

I don't understand mm internals including pte/ptl etc. , but I guess that
the direction is correct. Since the OOM reaper basically does

  Set MMF_UNSTABLE flag on mm_struct.
  For each reapable page in mm_struct {
    Take ptl lock.
    Remove pte.
    Release ptl lock.
  }

the page fault handler will need to check MMF_UNSTABLE with lock held.

  For each faulted page in mm_struct {
    Take ptl lock.
    Add pte only if MMF_UNSTABLE flag is not set.
    Release ptl lock.
  }

WARNING: multiple messages have this Message-ID
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: mhocko@kernel.org
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
	wenwei.tww@alibaba-inc.com, oleg@redhat.com, rientjes@google.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm, oom: fix potential data corruption when oom_reaper races with writer
Date: Sat, 5 Aug 2017 01:49:17 +0900	[thread overview]
Message-ID: <201708050149.JEC09861.MOLFtQFFVJOSOH@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20170804145631.GP26029@dhcp22.suse.cz>

Michal Hocko wrote:
> And that's why we still see the corruption. That, however, means that
> the MMF_UNSTABLE implementation has to be more complex and we have to
> hook into all anonymous memory fault paths which I hoped I could avoid
> previously.

I don't understand mm internals including pte/ptl etc. , but I guess that
the direction is correct. Since the OOM reaper basically does

  Set MMF_UNSTABLE flag on mm_struct.
  For each reapable page in mm_struct {
    Take ptl lock.
    Remove pte.
    Release ptl lock.
  }

the page fault handler will need to check MMF_UNSTABLE with lock held.

  For each faulted page in mm_struct {
    Take ptl lock.
    Add pte only if MMF_UNSTABLE flag is not set.
    Release ptl lock.
  }

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  reply	other threads:[~2017-08-04 16:49 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-03 13:59 [PATCH] mm, oom: fix potential data corruption when oom_reaper races with writer Michal Hocko
2017-08-03 13:59 ` Michal Hocko
2017-08-04  6:46 ` Tetsuo Handa
2017-08-04  7:42   ` Michal Hocko
2017-08-04  7:42     ` Michal Hocko
2017-08-04  8:25     ` Tetsuo Handa
2017-08-04  8:32       ` Michal Hocko
2017-08-04  8:32         ` Michal Hocko
2017-08-04  8:33         ` [PATCH 1/2] mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS Michal Hocko
2017-08-04  8:33           ` Michal Hocko
2017-08-04  8:33           ` [PATCH 2/2] mm, oom: fix potential data corruption when oom_reaper races with writer Michal Hocko
2017-08-04  8:33             ` Michal Hocko
2017-08-04  9:16       ` Re: [PATCH] " Michal Hocko
2017-08-04  9:16         ` Michal Hocko
2017-08-04 10:41         ` Tetsuo Handa
2017-08-04 10:41           ` Tetsuo Handa
2017-08-04 11:00           ` Michal Hocko
2017-08-04 11:00             ` Michal Hocko
2017-08-04 14:56             ` Michal Hocko
2017-08-04 14:56               ` Michal Hocko
2017-08-04 16:49               ` Tetsuo Handa [this message]
2017-08-04 16:49                 ` Tetsuo Handa
2017-08-05  1:46               ` 陶文苇
2017-08-05  1:46                 ` 陶文苇

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