linux-kernel - Re: [PATCH] more ZERO_PAGE handling ( was 2.6.24 regression: deadlock on coredump of big process)

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Date:	Wed, 7 May 2008 11:27:07 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Nick Piggin <npiggin@...e.de>,
	Mika Penttilä <mika.penttila@...umbus.fi>,
	Tony Battersby <tonyb@...ernetics.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] more ZERO_PAGE handling ( was 2.6.24 regression:
 deadlock on coredump of big process)

On Wed, 7 May 2008 11:14:04 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> > >  	pte = *ptep;
> > > -	if (!pte_present(pte))
> > > +	if (!pte_present(pte)) {
> > > +		if (!(flags & FOLL_WRITE) && pte_none(pte)) {
> > > +			pte_unmap_unlock(ptep, ptl);
> > > +			goto null_or_zeropage;
> > > +		}
> > >  		goto unlock;
> > > +	}
> > 
> > Just a small nitpick: I guess you don't need this FOLL_WRITE test because
> > null_or_zeropage will test FOLL_ANON which implies !FOLL_WRITE. It should give
> > slightly smaller code.
> > 
> > Otherwise, looks good to me:
> > 
> Hmm, but 
> 
> do_execve()
>   -> copy_strings()
>        -> get_arg_page()
>             -> get_user_pages()
> 
> can do write-page-fault in ANON (and it's a valid ops.)
> 
> So, I think it's safe not to remove FOLL_WRITE check here.
> 
BTW, in above case, returning ZERO_PAGE() when pgd/pud/pmd is not available is
safe ? (above path is expanding-stack at exec.)

Thanks,
-Kame




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