linux-kernel - Re: [PATCH] ext4: fix a big-endian bug when an extent is zeroed out

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Message-ID: <20130403122058.GB7741@thunk.org>
Date:	Wed, 3 Apr 2013 08:20:58 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>,
	Christian Kujau <lists@...dbynature.de>,
	CAI Qian <caiqian@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-s390 <linux-s390@...r.kernel.org>,
	Steve Best <sbest@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: fix a big-endian bug when an extent is zeroed out

On Wed, Apr 03, 2013 at 06:22:04PM +0800, Zheng Liu wrote:
> Subject: [PATCH] ext4: fix a big-endian bug when an extent is zeroed out
> 
> From: Zheng Liu <wenqing.lz@...bao.com>
> 
> When an extent was zeroed out, we forgot to do convert from cpu to le16.
> It could make us hit a BUG_ON when we try to write dirty pages out.  So
> fix it.
> 
> Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>

Thanks for finding this!  I think we should push this to Linus right
away, and not wait for the next merge window.  The bug has been here
for a long time, but it was unmasked by the fact that we unbroke
extent zeroing in 3.9-rcX.

I have two big questions.  (1) Shouldn't Eric Whitney have picked this
up with his ARM pandaboard testing, since IIRC it's big-endian as
well?  If not, is there something we can do to improve our testing wrt
to big-endian systems?

And (2) does it make sense to have an inline function
ext4_ext_set_len(len)?  It might save some lines of code, but more
importantly, it might make it less likely that we will overlook this
sort of bug in the future.

					- Ted
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