linux-kernel - Re: [PATCH] mm: fix page_mkclean_one (was: 2.6.19 file content corruption on ext3)

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Message-Id: <1166692586.27750.4.camel@localhost>
Date:	Thu, 21 Dec 2006 10:16:26 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Linus Torvalds <torvalds@...l.org>,
	Martin Michlmayr <tbm@...ius.com>,
	Hugh Dickins <hugh@...itas.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrei Popa <andrei.popa@...eo.ro>,
	Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Florian Weimer <fw@...eb.enyo.de>,
	Marc Haber <mh+linux-kernel@...schlus.de>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Arnd Bergmann <arnd.bergmann@...ibm.com>,
	gordonfarquharson@...il.com
Subject: Re: [PATCH] mm: fix page_mkclean_one (was: 2.6.19 file content
	corruption on ext3)

On Thu, 2006-12-21 at 00:03 +0100, Peter Zijlstra wrote:
> current version

Nitpicking ..

> @@ -444,17 +444,18 @@ static int page_mkclean_one(struct page
>  	if (!pte)
>  		goto out;
> 
> -	if (!pte_dirty(*pte) && !pte_write(*pte))
> -		goto unlock;
> +	while (pte_dirty(*pte) || pte_write(*pte)) {
> +		pte_t entry;
> 
> -	entry = ptep_get_and_clear(mm, address, pte);
> -	entry = pte_mkclean(entry);
> -	entry = pte_wrprotect(entry);
> -	ptep_establish(vma, address, pte, entry);
> -	lazy_mmu_prot_update(entry);
> -	ret = 1;
> +		flush_cache_page(vma, address, pte_pfn(*pte));
> +		entry = ptep_clear_flush(vma, address, pte);
> +		entry = pte_wrprotect(entry);
> +		entry = pte_mkclean(entry);
> +		ptep_establish(vma, address, pte, entry);

Now you are flushing the tlb twice. ptep_clear_flush clears the pte and
flushes the tlb, ptep_establish sets the new pte and flushes the tlb.
Not good. Use set_pte_at instead of the ptep_establish.

> +		lazy_mmu_prot_update(entry);
> +		ret = 1;
> +	}
> 
> -unlock:
>  	pte_unmap_unlock(pte, ptl);
>  out:
>  	return ret;

-- 
blue skies,
  Martin.

Martin Schwidefsky
Linux for zSeries Development & Services
IBM Deutschland Entwicklung GmbH

"Reality continues to ruin my life." - Calvin.


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