linux-kernel - Re: 2.6.36 io bring the system to its knees

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Date:	Wed, 10 Nov 2010 09:55:11 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Pavel Machek <pavel@....cz>, Dave Chinner <david@...morbit.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>, dave b <db.pub.mail@...il.com>,
	Sanjoy Mahajan <sanjoy@...n.edu>,
	Jesper Juhl <jj@...osbits.net>,
	Chris Mason <chris.mason@...cle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Aidar Kultayev <the.aidar@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, Ted Ts'o <tytso@....edu>,
	Corrado Zoccolo <czoccolo@...il.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Steven Barrett <damentz@...il.com>
Subject: Re: 2.6.36 io bring the system to its knees

On Wed, Nov 10, 2010 at 03:27:21PM +0100, Ingo Molnar wrote:
> That is data that was freshly touched around the time the system went down, right?
> 
> I.e. data that was probably half-modified by user-space to begin with.

It's data that wasn't synced out yet, yes.  Which isn't the problem per
se.  With ext3/4 in ordered mode, or xfs, or btrfs the file size won't
be incremented until the data is written.  in ext3/4 in writeback mode
(or various non-journaling filesystems) however the inode size is
updated, and metadagta changes are logged.  Besides exposing stale
data which is a security risk in multi-user systems it also means the
inode looks modified (by size and timestamps), but contains other data
than actually written.

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