linux-kernel - Re: [patch 1/9] fs: libfs buffered write leak fix

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Message-ID: <20070203174947.GA2656@lazybastard.org>
Date:	Sat, 3 Feb 2007 17:49:47 +0000
From:	Jörn Engel <joern@...ybastard.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Filesystems <linux-fsdevel@...r.kernel.org>,
	Linux Memory Management <linux-mm@...ck.org>
Subject: Re: [patch 1/9] fs: libfs buffered write leak fix

On Sat, 3 February 2007 02:33:16 +0100, Nick Piggin wrote:
> 
> If doing a partial-write, simply clear the whole page and set it uptodate
> (don't need to get too tricky).

That sounds just like a bug I recently fixed in logfs.  prepare_write()
would clear the page, commit_write() would write the whole page.  Bug
can be reproduced with a simple testcate:

echo -n foo > foo
echo -n bar >> foo
cat foo

With the bug, the second write will replace "foo" with "\0\0\0" and
cat will return "bar".  Doing a read instead of clearing the page will
return "foobar", as would be expected.

Can you hit the same bug with your patch or did I miss something?

Jörn

-- 
When people work hard for you for a pat on the back, you've got
to give them that pat.
-- Robert Heinlein
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