linux-kernel - Re: 2.6.19 file content corruption on ext3

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Date:	Mon, 18 Dec 2006 12:14:35 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Andrei Popa <andrei.popa@...eo.ro>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hugh@...itas.com>,
	Florian Weimer <fw@...eb.enyo.de>,
	Marc Haber <mh+linux-kernel@...schlus.de>,
	Martin Michlmayr <tbm@...ius.com>
Subject: Re: 2.6.19 file content corruption on ext3

On Mon, 18 Dec 2006, Andrei Popa wrote:
> 
> I dropped that patch and added WARN_ON(1), the unified patch is
> attached.
> 
> I got corruption: "Hash check on download completion found bad chunks,
> consider using "safe_sync"."

Ok. That is actually _very_ interesting.

It's interesting because (a) the corruption obviously goes away with the 
one-liner that effectively disables "page_mkclean_one()".

So that tells us that yes, it's a PTE dirty bit that matters.

But at the same time, it's interesting that it still happens when we try 
to re-add the dirty bit. That would tell me that it's one of two cases:

 - there is another caller of page cleaning that should have done the same 
   thing (we could check that by just doing this all _inside_ the 
   page_mkclean() thing)

OR:

 - page_mkclean_one() is simply buggy.

And I'm starting to wonder about the second case. But it all LOOKS really 
fine - I can't see anything wrong there (it uses the extremely 
conservative "ptep_get_and_clear()", and seems to flush everything right 
too, through "ptep_establish()").

		Linus
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