Re: [PATCH] mm, oom: fix potential data corruption when oom_reaper races with writer

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

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.
  }