linux-kernel - Re: [RFC PATCH v2 3/3] mm, oom: hand over MMF_OOM_SKIP to exit path if it is guranteed to finish

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Message-ID: <20181030063136.GU32673@dhcp22.suse.cz>
Date:   Tue, 30 Oct 2018 07:31:36 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     linux-mm@...ck.org, Roman Gushchin <guro@...com>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 3/3] mm, oom: hand over MMF_OOM_SKIP to exit path
 if it is guranteed to finish

On Tue 30-10-18 13:45:22, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > @@ -3156,6 +3166,13 @@ void exit_mmap(struct mm_struct *mm)
> >                 vma = remove_vma(vma);
> >         }
> >         vm_unacct_memory(nr_accounted);
> > +
> > +       /*
> > +        * Now that the full address space is torn down, make sure the
> > +        * OOM killer skips over this task
> > +        */
> > +       if (oom)
> > +               set_bit(MMF_OOM_SKIP, &mm->flags);
> >  }
> > 
> >  /* Insert vm structure into process list sorted by address
> 
> I don't like setting MMF_OOF_SKIP after remove_vma() loop. 50 users might
> call vma->vm_ops->close() from remove_vma(). Some of them are doing fs
> writeback, some of them might be doing GFP_KERNEL allocation from
> vma->vm_ops->open() with a lock also held by vma->vm_ops->close().
> 
> I don't think that waiting for completion of remove_vma() loop is safe.

What do you mean by 'safe' here?
-- 
Michal Hocko
SUSE Labs