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SubjectRe: btrfs zero divide (was: Re: Linux 3.10 problem reports (yes, plural))
On Tue, Jul 30, 2013 at 11:07:30AM +0200, Geert Uytterhoeven wrote:
> On Tue, 30 Jul 2013, Thorsten Glaser wrote:
> > NEW problem: btrfs doesn’t work at all. I had to reboot my
> > buildd into 3.2 using echo s/u/s/o >/proc/sysrq-trigger as
> > the attempt to mount it left the system hanging there.
>
> > [ 0.000000] Linux version 3.10-1-m68k (debian-kernel@lists.debian.org) (gcc version 4.8.1 (Debian 4.8.1-7+m68k.1) ) #1 Debian 3.10.3-1 (2013-07-27)
>
> > [ 6.720000] bio: create slab <bio-1> at 1
> > [ 6.740000] Btrfs loaded
> > [ 6.830000] device label ara5-butter devid 1 transid 376178 /dev/nfhd8p3
> > [ 7.150000] EXT4-fs (nfhd8p1): mounted filesystem with ordered data mode. Opts: (null)
> > [ 14.520000] udevd[228]: starting version 175
> > [ 17.820000] device label ara5-butter devid 1 transid 376178 /dev/nfhd8p3
> > [ 20.850000] Adding 3670012k swap on /dev/nfhd8p2. Priority:-1 extents:1 across:3670012k
> > [ 21.380000] EXT4-fs (nfhd8p1): re-mounted. Opts: (null)
> > [ 31.300000] EXT4-fs (nfhd8p1): re-mounted. Opts: errors=remount-ro
> > [ 38.460000] device label ara5-butter devid 1 transid 376178 /dev/nfhd8p3
> > [ 38.530000] btrfs: setting nodatacow, compression disabled
> > [ 38.540000] btrfs: enabling auto recovery
> > [ 38.570000] btrfs: disk space caching is enabled
> > [ 38.600000] *** ZERO DIVIDE *** FORMAT=2
> > [ 38.630000] Current process id is 722
> > [ 38.660000] BAD KERNEL TRAP: 00000000
> > [ 38.680000] Modules linked in: evdev mac_hid ext4 crc16 jbd2 mbcache btrfs xor lzo_compress zlib_deflate raid6_pq crc32c libcrc32c
> > [ 38.730000] PC: [<319535b2>] __btrfs_map_block+0x11c/0x119a [btrfs]
>
> Woops, adding the btrfs devs to CC.
>

Can you gdb btrfs.ko and do

list *(__btrfs_map_block+0x11c)

so I can see where this is? I've not seen this yet, just so I'm clear this is
blowing up because we're doing

blah / 0

right? I've looked at all the places we do divides in this function and it
doesn't look like we're doing this anywhere but I could be blind. Thanks,

Josef
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