Re: System crash while scrubbing on 3.18.x

[Cameron Berkenpas <cam@neo-zeon.de>]

Hello,

I should have mentioned this earlier. I get absolutely nothing in the 
logs. I can't look at dmesg either as the system is completely unresponsive.

On 03/06/2015 04:30 AM, Liu Bo wrote:
> On Thu, Mar 05, 2015 at 05:18:21PM -0800, Cameron Berkenpas wrote:
>> Hello,
>>
>> Sorry for the long email...
>>
>> I've found my system locks up when scrubbing with 3.18.x, but not
>> with 3.17.8 across 2 systems.
>>
>> I have the following BTRFS partitions on system 1:
>> /  (128GiB, 49GiB used on SSD)
>> /home (4.2TiB, 624GB used on HDD RAID volume)
>>
>> I have the following BTRFS partitions on system 2:
>> / (196GiB, 17GiB used on HDD RAID volume)
>> /home (7.1TiB, 2.9TiB used on HDD RAID volume)
>>
>> My OS is Netrunner 15 (which 98% Kubuntu) on system 1, and
>> up-to-date debian testing on system 2.
>>
>> I've never encountered a lock up while scrubbing /. Just with /home.
>>
>> The systems never lock up immediately, but takes some time. VERY
>> rarely I'll see the lockup when the scrub is at <100GiB completed.
>> Typically it happens somewhere between 200-350GiB. A few times it's
>> gone beyond 500GiB. This is probably why I've never encountered the
>> issue with /, it's just not big enough on either system.
>>
>> Both systems were otherwise idle while performing the scrubs that
>> crashed the systems.
>>
>> /home is on a partition on a RAID10 volume on a 3ware 9740-4i
>> controller with 4x 3TB disks on system 1. On system 2, it's the same
>> controller but with 4x 4TB disks (and / on system 2 is a partition
>> on the same RAID volume rather than a separate disk). Both systems
>> have 32GiB memory, and the otherwise the hardware is pretty
>> different between the systems (AMD Vs. Intel, etc).
>>
>> I suspect that the RAID controller probably isn't relevant. Both
>> arrays and their drives are healthy.
>>
>> I've also encountered the issue on a freshly formatted filesystem
>> with my data copied from a backup on system 1.
>>
>> I've tried tried scrubbing with btrfs-progs 3.17 (installed from the
>> distribution repos on both systems), and btrfs-progs from git (using
>> tag v3.18.x). Neither version made a difference.
>>
>> In case this is helpful to anyone, here's how I've discovered the issue:
>> I decided to test btrfs with bcache on system 1 to see if the
>> stability had improved since I'd tried bcache+btrfs about a year
>> ago. I backed up /home on system 1 and then freshly formatted it and
>> set it to use bcache. I was running Linux 3.18.8 and encountered the
>> problem that I've described above. I assumed the bcache+btrfs
>> combination was still broken so I formatted the system again (this
>> time still using btrfs, but without bcache) and copied all my files
>> back. I encountered the same issue without bcache. Realizing the
>> issue wasn't bcache related, I did ANOTHER format, this time back to
>> bcache+btrfs.
>>
>>  From here in my testing, I found that system 2 (which has no bcache)
>> also crashed when scrubbing with Linux 3.18.8. I decided to try
>> 3.17.8 on system 1 (since 3.18.8 seemed to be the common denominator
>> between the 2 systems), found that fixed the issue, and then
>> downgraded system 2 to use 3.17.8 as well, which also fixed the
>> issue there.
>>
>> (Note: At one point I also tried Linux 3.18.7 and 3.18.5, however,
>> those kernels are affected by the scrub/crash issue as well.)
>>
>> I found something else interesting when I tested against Linux
>> 3.19.0. With 3.19.0, the bcache system always crashes fairly early
>> in the scrub (<100GiB), but the non-bcache system has no issues.
>> This suggests my problem with 3.19.0 is a bcache+btrfs issue (or
>> simply an issue with bcache).
>>
>> I'm not sure if bcache is relevant to the BTRFS devs at this point,
>> but I thought I'd put that there for anyone who might find that
>> information useful.
>>
>> To summarize:
>> I've tested with 2 systems, and scrubbing caused crashes occurred on
>> both with Linux 3.18.8, but not with 3.17.8 for both systems
>> I've tested 1 system with and without bcache, and bcache made no
>> difference between Linux 3.17.8 and 3.18.8.
>> I've tested with 3.19.0, and I crash when scrubbing on the bcache
>> system, but not the non-bcache system.
> Better to have some stacks about the scrub crash.
>
> Thanks,
>
> -liubo
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html