linux-ext4 - RE: ext4: what are possible causes of "zero length extent" ?

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Date:	Mon, 23 May 2016 10:48:35 +0000
From:	"Craske, Mark" <Mark_Craske@...tor.com>
To:	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>
Subject: RE: ext4: what are possible causes of "zero length extent" ?

Hello Ted and Andreas,

We are still getting instances of "zero length extent" ext4 file system corruptions.
Are there any know causes, and are any of those fixes by upstream kernel patches?

Regards,
Mark Craske
Embedded Software Engineer
Linux Transportation Solutions 

Mentor Graphics (UK) Ltd., Rivergate, Newbury Business Park, London Road, Newbury, RG14 2QB, UK
 
Tel: +44 (0)1635 81 1436
Mobile : +44 (0)7900 008 230
E-mail : Mark_Craske@...tor.com
Yahoo-IM: mcraske_uk   Skype: mcraske_uk

> -----Original Message-----
> From: linux-ext4-owner@...r.kernel.org [mailto:linux-ext4-
> owner@...r.kernel.org] On Behalf Of Craske, Mark
> Sent: 11 May 2016 11:22
> To: linux-ext4@...r.kernel.org; Theodore Ts'o; Andreas Dilger
> Subject: ext4: what are possible causes of "zero length extent" ?
> 
> Hello ext4 maintainers,
> 
> This is somewhat of a follow-on from the "ext4 filesystem bad extent error
> review"
> thread from 2014.
> 
> Embedded system with main SoC Freescale i.MX6(ARM cortex A9), dual CPU,
> running kernel 3.8.13.28, storage device is eMMC.
> This still suffers from "zero length extent" ext4 file system corruptions.
> 
> I looked for upstream patches, but did not find any that explicitly fix "zero
> length extent"
> problems apart from "2f97486 ext4: check for zero length extent explicitly".
> That patch prevents the kernel panics but makes the affected file unreadable
> and unremovable, which can be fixed by running fsck.
> 
> What are possible causes of "zero length extent", and are there upstream
> patches that actually deal with some of those?
> 
> Regards,
> Mark Craske
> Mentor Graphics (UK) Ltd.
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