Attempt to change raid1 to raid0 results in division error in kernel

Attempt to change raid1 to raid0 results in division error in kernel

[Robert Goliasz]

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Hi,

When attempting to change raid level from 1 to 0 (I was doing some testing
trying to convert a raid1 array to a raid10 one), I got a division error.

I'm on Debian sid, output of uname -a is:

  Linux gbl-macbook 3.2.0-4-amd64 #1 SMP Debian 3.2.35-2 x86_64 GNU/Linux

I had the following raid set up (using devices on LVM):

  gbl-macbook# cat /proc/mdstat 
  Personalities : [raid1] [raid0] [raid10] 
  md0 : active raid1 md1[2] md2[1]
        409280 blocks super 1.2 [2/2] [UU]
        
  md2 : active raid0 dm-8[1] dm-7[0]
        1022976 blocks super 1.2 512k chunks
        
  md1 : active raid0 dm-6[1] dm-5[0]
        1022976 blocks super 1.2 512k chunks
        
  unused devices: <none>

/dev/md0 was a mounted ext4 filesystem.

I attempted to run this:

  gbl-macbook# mdadm --grow /dev/md0 -l 0
  zsh: segmentation fault  mdadm --grow /dev/md0 -l 0
  gbl-macbook# 

All my terminals have shown the following alert:

  Message from syslogd@gbl-macbook at May 23 11:26:11 ...
   kernel:[569106.802042] divide error: 0000 [#1] SMP 
  
  Message from syslogd@gbl-macbook at May 23 11:26:11 ...
   kernel:[569106.802393] Stack:
  
  Message from syslogd@gbl-macbook at May 23 11:26:11 ...
   kernel:[569106.802430] Call Trace:
  
  Message from syslogd@gbl-macbook at May 23 11:26:11 ...
   kernel:[569106.802519] Code: 4c 24 18 49 8b 6c 24 18 48 89 4c 24 18 eb 6b 48 8b 7d 30 48 8d 74 24 38 e8 d4 16 af e0 49 63 8c 24 bc 00 00 00 48 8b 45 10 31 d2 <48> f7 f1 48 0f af c1 48 89 45 10 4d 8b 6c 24 18 eb 2f 49 8b 7d 
  
Here's the relevant output from dmesg:

  [569106.729859] RAID1 conf printout:
  [569106.729870]  --- wd:1 rd:2
  [569106.729878]  disk 0, wo:0, o:1, dev:md1
  [569106.734368] md: unbind<md2>
  [569106.795283] md: export_rdev(md2)
  [569106.802042] divide error: 0000 [#1] SMP 
  [569106.802053] CPU 0 
  [569106.802057] Modules linked in: raid10 raid0 ext4 jbd2 mbcache raid1 md_mod b43 bcma asix usbnet mii nls_cp437 vfat fat nls_utf8 hfsplus usb_storage cdc_acm snd_usb_audio snd_usbmidi_lib ip6table_filter ip6_tables iptable_filter ip_tables ebtable_nat ebtables x_tables parport_pc ppdev lp parport rfcomm bnep pci_stub cpufreq_stats vboxpci(O) cpufreq_userspace cpufreq_powersave cpufreq_conservative vboxnetadp(O) vboxnetflt(O) vboxdrv(O) binfmt_misc uinput nfsd nfs nfs_acl auth_rpcgss fscache lockd sunrpc loop firewire_sbp2 fuse kvm_intel kvm uvcvideo videodev v4l2_compat_ioctl32 media snd_hda_codec_hdmi btusb bluetooth crc16 bcm5974 snd_hda_codec_cirrus joydev snd_hda_intel snd_hda_codec snd_pcm_oss snd_hwdep snd_mixer_oss snd_pcm snd_page_alloc snd_seq_midi snd_seq_midi_event snd_rawmidi arc4 snd_seq snd_seq_device snd_timer coretemp mac80211 cfg80211 rfkill ssb rng_core applesmc pcmcia i2c_i801 pcmcia_core crc32c_intel snd iTCO_wdt acpi_cpufreq soundcore ghash_clmulni_intel aesni_intel aes_x86_64 aes_generic evdev i2c_core iTCO_vendor_support mperf cryptd input_polldev pcspkr fglrx(P) battery video ac apple_bl(O) button processor power_supply thermal_sys xfs hid_microsoft dm_mod sg sr_mod sd_mod cdrom crc_t10dif ata_generic hid_apple usbhid hid uhci_hcd ata_piix libata firewire_ohci scsi_mod firewire_core crc_itu_t sdhci_pci ehci_hcd sdhci mmc_core tg3 usbcore libphy usb_common [last unloaded: bcma]
  [569106.802283] 
  [569106.802290] Pid: 30710, comm: mdadm Tainted: P           O 3.2.0-4-amd64 #1 Debian 3.2.35-2 Apple Inc. MacBookPro8,2/Mac-94245A3940C91C80
  [569106.802302] RIP: 0010:[<ffffffffa065745b>]  [<ffffffffa065745b>] create_strip_zones+0x71/0x491 [raid0]
  [569106.802320] RSP: 0018:ffff8801a8a77d48  EFLAGS: 00010246
  [569106.802325] RAX: 00000000001f3600 RBX: ffff88012ccf5920 RCX: 0000000000000000
  [569106.802331] RDX: 0000000000000000 RSI: fffffffffffffffb RDI: ffff88025151540c
  [569106.802337] RBP: ffff880254d2f000 R08: 00000000fffffffd R09: ffff88025151ffff
  [569106.802343] R10: ffffffff81600000 R11: ffffffff81600000 R12: ffff88042f058c00
  [569106.802349] R13: ffff8801beb09000 R14: 0000000000000005 R15: ffff88042f058c18
  [569106.802356] FS:  00007f6027661700(0000) GS:ffff88046fa00000(0000) knlGS:0000000000000000
  [569106.802363] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
  [569106.802368] CR2: 000000000041f820 CR3: 00000001916d0000 CR4: 00000000000406f0
  [569106.802375] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  [569106.802381] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
  [569106.802388] Process mdadm (pid: 30710, threadinfo ffff8801a8a76000, task ffff880116fee380)
  [569106.802393] Stack:
  [569106.802397]  00000000fffffff4 0000000000000001 0000000000000001 ffff88042f058c18
  [569106.802408]  0000000000000000 ffff8801a8a77e10 ffff8801a8a77e28 ffff88010031646d
  [569106.802419]  30646961722d646d ffff880100000000 ffff88046fdfcc08 0000004081109b2e
  [569106.802430] Call Trace:
  [569106.802442]  [<ffffffffa0657b11>] ? raid0_takeover+0x1c3/0x1e5 [raid0]
  [569106.802456]  [<ffffffffa066d409>] ? level_store+0x21b/0x52b [md_mod]
  [569106.802470]  [<ffffffffa066ec77>] ? md_attr_store+0x9a/0xbc [md_mod]
  [569106.802483]  [<ffffffff8114e4e7>] ? sysfs_write_file+0xe0/0x11c
  [569106.802494]  [<ffffffff810f9cc5>] ? vfs_write+0xa2/0xe9
  [569106.802502]  [<ffffffff810f9ea2>] ? sys_write+0x45/0x6b
  [569106.802515]  [<ffffffff81352012>] ? system_call_fastpath+0x16/0x1b
  [569106.802519] Code: 4c 24 18 49 8b 6c 24 18 48 89 4c 24 18 eb 6b 48 8b 7d 30 48 8d 74 24 38 e8 d4 16 af e0 49 63 8c 24 bc 00 00 00 48 8b 45 10 31 d2 <48> f7 f1 48 0f af c1 48 89 45 10 4d 8b 6c 24 18 eb 2f 49 8b 7d 
  [569106.802594] RIP  [<ffffffffa065745b>] create_strip_zones+0x71/0x491 [raid0]
  [569106.802604]  RSP <ffff8801a8a77d48>
  [569106.802688] ---[ end trace dc1acf1d4fa82dd5 ]---

Afterwards, my mounted filesystem (/dev/md0) disappeared (it's no longer
mounted), and all operations related to software raid seem to fail:

  gbl-macbook# umount /dev/md0
  ^C^C^C^C
  <hangs forever>

  11:41:38 goblin@gbl-macbook:~ % cat /proc/mdstat 
  <hangs forever but is Ctrl-Cable>

I haven't attempted to re-produce this yet.

-- 
Robert Goliasz
Infrastructure Engineer

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Re: Attempt to change raid1 to raid0 results in division error in kernel

[Stan Hoeppner]

On 5/23/2013 5:44 AM, Robert Goliasz wrote:
> Hi,
> 
> When attempting to change raid level from 1 to 0 

I don't even know if this is possible.

> (I was doing some testing
> trying to convert a raid1 array to a raid10 one), I got a division error.
...
>   gbl-macbook# mdadm --grow /dev/md0 -l 0

If it is possible, this command line won't work because you didn't
specify a chunk size for the RAID0 stripe.  Every striped array type
requires a chunk size.

>   zsh: segmentation fault  mdadm --grow /dev/md0 -l 0
>   gbl-macbook# 
...

> Afterwards, my mounted filesystem (/dev/md0) disappeared (it's no longer
> mounted), and all operations related to software raid seem to fail:

Well of course.  Experimenting with mdadm without knowing what you're
doing will often result in lost/corrupted arrays and other forms of damage.

At this point you should simply start a new thread and ask:

"How do I convert a RAID1 array to RAID0?"

or

"How do I convert a RAID1 array to RAID10?"

instead of working backwards from your mistakes here.

-- 
Stan

Re: Attempt to change raid1 to raid0 results in division error in kernel

[Robert Goliasz]

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Hi Stan,

Thanks for your reply.

The point of my thread was to point out that a userland tool shouldn't
be able to cause a kernel to crash. It also shouldn't segfault when given
incorrect arguments.

If conversion from raid1 to raid0 is supported but I didn't specify
the right arguments, I should get an appropriate error message. If it's
not supported, then I should also get an appropriate error message.
My machine shouldn't crash because of me giving wrong arguments to mdadm.

Another, smaller, issue is that if conversion from raid 1 to raid 0 is
not supported then perhaps the mdadm manpage should be clearer about it,
rather saying "Currently supported growth options [...] [are] changing the
RAID level between 0, 1, 5, and 6"

>>   gbl-macbook# mdadm --grow /dev/md0 -l 0
>If it is possible, this command line won't work because you didn't
>specify a chunk size for the RAID0 stripe.  Every striped array type
>requires a chunk size.

This doesn't seem to be correct, I'm able to at least create a RAID0 stripe
without specifying the chunk size explicitly:

  root@gbl-macbook:~# mdadm --create /dev/md1 -l 0 -n 2 /dev/vg0/v1 /dev/vg0/v2
  mdadm: /dev/vg0/v1 appears to be part of a raid array:
      level=raid1 devices=3 ctime=Thu May 23 11:13:33 2013
  Continue creating array? y
  mdadm: Defaulting to version 1.2 metadata
  mdadm: array /dev/md1 started.
  root@gbl-macbook:~# cat /proc/mdstat 
  Personalities : [raid0] 
  md1 : active raid0 dm-4[1] dm-3[0]
        203776 blocks super 1.2 512k chunks
        
  unused devices: <none>
  root@gbl-macbook:~# 


>> Afterwards, my mounted filesystem (/dev/md0) disappeared (it's no longer
>> mounted), and all operations related to software raid seem to fail:
>Well of course.  Experimenting with mdadm without knowing what you're
>doing will often result in lost/corrupted arrays and other forms of damage.

I knew exactly what I was doing. I was testing whether conversion from raid1
to raid0 was supported. I got an unexpected result in the form of a kernel
crash. After discussing on IRC I was asked to report this here.

I've concluded that it's not supported or broken and will not attempt to run
this on a production machine.

-- 
Robert Goliasz
Infrastructure Engineer

-- 
******************************************************************************** 
  
DISCLAIMER: This e-mail is confidential and should not be used by anyone 
who is
not the original intended recipient. If you have received this e-mail in 
error
please inform the sender and delete it from your mailbox or any other 
storage
mechanism. Neither Macmillan Publishers Limited nor any of its agents accept
liability for any statements made which are clearly the sender's own and not
expressly made on behalf of Macmillan Publishers Limited or one of its 
agents.
Please note that neither Macmillan Publishers Limited nor any of its agents
accept any responsibility for viruses that may be contained in this e-mail 
or
its attachments and it is your responsibility to scan the e-mail and 
attachments (if any). No contracts may be concluded on behalf of Macmillan 
Publishers Limited or its agents by means of e-mail communication. 
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Publishers Limited Registered in England and Wales with registered number 
785998 
Registered Office Brunel Road, Houndmills, Basingstoke RG21 6XS   
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Re: Attempt to change raid1 to raid0 results in division error in kernel

[NeilBrown]

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On Thu, 23 May 2013 11:44:00 +0100 Robert Goliasz
<r.goliasz@digital-science.com> wrote:

> Hi,
> 
> When attempting to change raid level from 1 to 0 (I was doing some testing
> trying to convert a raid1 array to a raid10 one), I got a division error.
> 
> I'm on Debian sid, output of uname -a is:
> 
>   Linux gbl-macbook 3.2.0-4-amd64 #1 SMP Debian 3.2.35-2 x86_64 GNU/Linux
....
> I attempted to run this:
> 
>   gbl-macbook# mdadm --grow /dev/md0 -l 0
>   zsh: segmentation fault  mdadm --grow /dev/md0 -l 0
>   gbl-macbook# 
> 
> All my terminals have shown the following alert:
> 
>   Message from syslogd@gbl-macbook at May 23 11:26:11 ...
>    kernel:[569106.802042] divide error: 0000 [#1] SMP 

Fixed by commit 24b961f811a3e790a9b93604d25 which is in linux-3.4


http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=24b961f811a3e790a9b93604d25

NeilBrown

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