linux-kernel - Re: btrfs zero divide

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Message-ID: <CAMuHMdWWz7EmU0-OyM+hnBss4AZjR30tLsRbBVsXF0cy2THMyA@mail.gmail.com>
Date:	Tue, 13 Aug 2013 14:12:04 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Andreas Schwab <schwab@...ux-m68k.org>
Cc:	Josef Bacik <jbacik@...ionio.com>, Thorsten Glaser <tg@...bsd.de>,
	Joe Perches <joe@...ches.com>,
	"Debian GNU/Linux m68k" <debian-68k@...ts.debian.org>,
	linux-btrfs@...r.kernel.org,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	linux-am33-list@...hat.com
Subject: Re: btrfs zero divide

On Fri, Aug 9, 2013 at 2:30 PM, Andreas Schwab <schwab@...ux-m68k.org> wrote:
> Andreas Schwab <schwab@...ux-m68k.org> writes:
>> Josef Bacik <jbacik@...ionio.com> writes:
>>> So stripe_len shouldn't be 0, if it is you have bigger problems :).

[ lost context: this is about the first do_div() in __btrfs_map_block() ]

>> The bigger problem is that stripe_nr is u64, this is completely bogus.
>> The first operand of do_div must be u32.  This goes through the whole
>> file.
>
> Of course, what I meant was that the *second* operand must be u32, but
> that doesn't change my point.

I checked all do_div() implementations, and (unless I missed one) m68k and
mn10300 were the only two that didn't truncate base to 32 bits.

Mn10300 is little endian, so I think the problem won't happen there.

Andreas, I'll apply your patch
(http://permalink.gmane.org/gmane.linux.ports.m68k/5008)
with the crash log added to the commit message, so it's appropriate for -stable.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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