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

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Message-ID: <Pine.LNX.4.64.0612171725110.3479@woody.osdl.org>
Date:	Sun, 17 Dec 2006 17:29:30 -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, Linus Torvalds wrote:
> 
> 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?

I think we discussed doing exactly this at some earlier time, actually, 
just to try to throttle people who do lots of page dirtying. 

Maybe we even do it somewhere, but I tried to see it, and in the normal 
"nopage()" routine we very much try to _avoid_ locking the page (ie if 
it's marked PageUptodate() we'll return it whether locked or not). Which 
is fine - especially for readers, there really isn't any reason to ever 
delay them getting access to a page just because it's locked for write-out 
or something (once it's mapped, they'll have access to it regardless of 
any locked state in the kernel anyway).

So I don't actually see any serialization at all that would keep a random 
page from being paged back in.

		Linus
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