From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f53.google.com ([209.85.220.53]:40211 "EHLO mail-pa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759531Ab3HNI4k (ORCPT ); Wed, 14 Aug 2013 04:56:40 -0400 MIME-Version: 1.0 In-Reply-To: References: <20130730171329.GF24583@localhost.localdomain> <20130730204001.GG24583@localhost.localdomain> <87eha33v9f.fsf@igel.home> <20130809180441.GB12314@lenny.home.zabbo.net> Date: Wed, 14 Aug 2013 10:56:40 +0200 Message-ID: Subject: Re: btrfs zero divide From: Geert Uytterhoeven To: Zach Brown , Andrew Morton Cc: Andreas Schwab , Josef Bacik , Thorsten Glaser , Joe Perches , "Debian GNU/Linux m68k" , linux-btrfs@vger.kernel.org, Linux Kernel Development , David Woodhouse , Chris Mason , scsi Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Wed, Aug 14, 2013 at 10:40 AM, Geert Uytterhoeven wrote: > On Tue, Aug 13, 2013 at 6:32 PM, Geert Uytterhoeven > wrote: >> On Fri, 9 Aug 2013, Zach Brown wrote: >>> On Fri, Aug 09, 2013 at 02:26:36PM +0200, Andreas Schwab wrote: >>> > Josef Bacik writes: >>> > >>> > > So stripe_len shouldn't be 0, if it is you have bigger problems :). >>> > >>> > 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. >> >> This was introduced by commit 53b381b3abeb86f12787a6c40fee9b2f71edc23b >> ("Btrfs: RAID5 and RAID6"), which changed the divisor from >> map->stripe_len (struct map_lookup.stripe_len is int) to a 64-bit >> temporary. >> >>> Definitely. Can we get some typeof() tricks in the macros to have the >>> build fail if (when, evidently) someone gets it wrong? >> >> Not using typeof, as there are way too many callsites where int is used >> instead of u32. >> >> However, checking that sizeof() equals to 4 seems to work. >> Below is a patch for asm-generic, which is untested, but it works when >> adding the same checks to arch/m68k/include/asm/div64.h >> >> This is not something we just want to drop in, as it has the potential of >> breaking lots of things (yes, it breaks btrfs :-) > > Found so far: > - Several calls to sector_div() in blkdev_issue_discard() > - Two calls to do_div() in sd_completed_bytes() > > Some of these even operate on dividends that never exceed 32-bit, tss... Two more: drivers/md/dm-cache-target.c:too_many_discard_blocks fs/jfs/jfs_dmap.c:dbDiscardAG These bring in the 64-bit divisor from somewhere else, so they're less trivial to fix. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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