linux-kernel - Re: Rampant ext3/4 corruption on 2.6.34-rc7 with VIVT ARM (Marvell 88f5182)

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Message-ID: <1273786425.21352.191.camel@pasglop>
Date:	Fri, 14 May 2010 07:33:45 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Saeed Bishara <saeed@...vell.com>,
	Nicolas Pitre <nico@...vell.com>, linux-ext4@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>
Subject: Re: Rampant ext3/4 corruption on 2.6.34-rc7 with VIVT ARM (Marvell
 88f5182)

On Thu, 2010-05-13 at 17:12 +0200, Jan Kara wrote:

> If you look at the array more in detail, you'll notice that 'offs' part of
> structure is sometimes identical. That should never happen because 'offs'
> contains offset of the corresponding directory entry in a block. So when
> offsets are identical in this array, subsequent move will copy some entries
> several times and leave entries that should be moved in the old block,
> resulting in a corruption we see.
>   The question is, how could offsets be the same? dx_make_map seems to get
> it right and dx_sort_map as well. Maybe I'd peek into disassembly of
> dx_sort_map to see whether swap() macro does what it should... If that
> looks OK, you could try adding some debug checks into dx_sort_map and try
> to catch the moment when duplicate offsets are created...

Thanks. I'll have a look. It could be a miscompile indeed. My cross-gcc
is a 4.4.0, maybe that's the root of the problem.

Cheers,
Ben.


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