linux-kernel - Re: [PATCH] mm, oom: fix potential data corruption when oom

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Message-Id: <201708041941.JFH26516.HOMtSQFFFOLVJO@I-love.SAKURA.ne.jp>
Date:   Fri, 4 Aug 2017 19:41:42 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     mhocko@...nel.org
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        wenwei.tww@...baba-inc.com, oleg@...hat.com, rientjes@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, oom: fix potential data corruption when oom_reaper races with writer

Michal Hocko wrote:
> On Fri 04-08-17 17:25:46, Tetsuo Handa wrote:
> > Well, while lockdep warning is gone, this problem is remaining.
> > 
> > diff --git a/mm/memory.c b/mm/memory.c
> > index edabf6f..1e06c29 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -3931,15 +3931,14 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> >         /*
> >          * This mm has been already reaped by the oom reaper and so the
> >          * refault cannot be trusted in general. Anonymous refaults would
> > -        * lose data and give a zero page instead e.g. This is especially
> > -        * problem for use_mm() because regular tasks will just die and
> > -        * the corrupted data will not be visible anywhere while kthread
> > -        * will outlive the oom victim and potentially propagate the date
> > -        * further.
> > +        * lose data and give a zero page instead e.g.
> >          */
> > -       if (unlikely((current->flags & PF_KTHREAD) && !(ret & VM_FAULT_ERROR)
> > -                               && test_bit(MMF_UNSTABLE, &vma->vm_mm->flags)))
> > +       if (unlikely(!(ret & VM_FAULT_ERROR)
> > +                    && test_bit(MMF_UNSTABLE, &vma->vm_mm->flags))) {
> > +               if (ret & VM_FAULT_RETRY)
> > +                       down_read(&vma->vm_mm->mmap_sem);
> >                 ret = VM_FAULT_SIGBUS;
> > +       }
> > 
> >         return ret;
> >  }
> 
> I have re-read your email again and I guess I misread previously. Are
> you saying that the data corruption happens with the both patches
> applied?

Yes. Data corruption still happens.