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

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Date:	Sun, 17 Dec 2006 17:22:57 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Andrew Morton <akpm@...l.org>
cc:	andrei.popa@...eo.ro,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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 Sun, 17 Dec 2006, Andrew Morton wrote:
> 
> From my quick reading, all callers of try_to_free_buffers() have already
> unmapped the page from pagetables, and given that the reported ext3 corruption
> happens on uniprocessor, non-preempt kernels, I doubt if this patch will fix
> things.

Hmm. One possible explanation: maybe the page actually _did_ get unmapped 
from the page tables, but got added back?

I don't think we lock the page when faulting it in (we want it to be 
uptodate, but not necessarily locked). So assuming the pageout sequence 
always _does_ follow the rule that it only does try_to_free_buffers() on 
pages that aren't mapped, what actually protects them from not becoming 
mapped (and dirtied) during that sequence?

So we should probably do a "wait_for_page()" in do_no_page()?

Or maybe only do it for write accesses (since we don't really care about 
getting mapped readably)? If so, we need to do it in the write case of 
do_no_page() _and_ in the do_wp_page() case. Hmm?

		Linus
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