linux-kernel - Re: [patch 2/4] vfs: add set_page_dirty

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Message-Id: <1234865116.4744.46.camel@laptop>
Date:	Tue, 17 Feb 2009 11:05:16 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Edward Shishkin <edward.shishkin@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ryan Hope <rmh3093@...il.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-kernel@...r.kernel.org,
	ReiserFS Mailing List <reiserfs-devel@...r.kernel.org>
Subject: Re: [patch 2/4] vfs: add set_page_dirty_notag

On Tue, 2009-02-17 at 10:38 +0100, Nick Piggin wrote:

> It is a great shame that filesystems are not properly notified
> that a page may become dirty before the actual set_page_dirty
> event (which is not allowed to fail and is called after the
> page is already dirty).

Not quite true, for example the set_page_dirty() done by the write fault
code is done _before_ the page becomes dirty.

This before/after thing was the reason for that horrid file corruption
bug that dragged on for a few weeks back in .19 (IIRC).

> This is a big problem I have with fsblock simply in trying to
> make the memory allocation robust. page_mkwrite unfortunately
> is racy and I've fixed problems there... the big problem though
> is get_user_pages. Fixing that properly seems to require fixing
> callers so it is not really realistic in the short term.

Right, I'm just not sure what we can do, even with a
prepage_page_dirty() function, what are you going to do, fail the fault?

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