Re: panic on 4.20 server exporting xfs filesystem

Eric Sandeen
2015-03-04T22:49:13Z

On 3/4/15 4:45 PM, Dave Chinner wrote:
> On Wed, Mar 04, 2015 at 05:27:09PM -0500, J. Bruce Fields wrote:
>> On Thu, Mar 05, 2015 at 09:09:00AM +1100, Dave Chinner wrote:
>>> On Wed, Mar 04, 2015 at 10:54:21AM -0500, J. Bruce Fields wrote:
>>>> On Tue, Mar 03, 2015 at 09:08:26PM -0500, J. Bruce Fields wrote:
>>>>> On Wed, Mar 04, 2015 at 09:44:56AM +1100, Dave Chinner wrote:
>>>>>> On Tue, Mar 03, 2015 at 05:10:33PM -0500, J. Bruce Fields wrote:
>>>>>>> I'm getting mysterious crashes on a server exporting an xfs filesystem.
>>>>>>>
>>>>>>> Strangely, I've reproduced this on
>>>>>>>
>>>>>>> 93aaa830fc17 "Merge tag 'xfs-pnfs-for-linus-3.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/dgc/linux-xfs
>>>>>>>
>>>>>>> but haven't yet managed to reproduce on either of its parents
>>>>>>> (24a52e412ef2 or 781355c6e5ae). That might just be chance, I'll try
>>>>>>> again.
>>>>>>
>>>>>> I think you'll find that the bug is only triggered after that XFS
>>>>>> merge because it's what enabled block layout support in the server,
>>>>>> i.e. nfsd4_setup_layout_type() is now setting the export type to
>>>>>> LAYOUT_BLOCK_VOLUME because XFS has added the necessary functions to
>>>>>> it's export ops.
>>>>>
>>>>> Doh--after all the discussion I didn't actually pay attention to what
>>>>> happened in the end. OK, I see, you're right, it's all more-or-less
>>>>> dead code till that merge.
>>>>>
>>>>> Christoph's code was passing all my tests before that, so maybe we
>>>>> broke something in the merge process.
>>>>>
>>>>> Alternatively, it could be because I've added more tests--I'll rerun my
>>>>> current tests on his original branch....
>>>>
>>>> The below is on Christoph's pnfsd-for-3.20-4 (at cd4b02e). Doesn't look
>>>> very informative. I'm running xfstests over NFSv4.1 with client and
>>>> server running the same kernel, the filesystem in question is xfs, but
>>>> isn't otherwise available to the client (so the client shouldn't be
>>>> doing pnfs).
>>>>
>>>> --b.
>>>>
>>>> BUG: unable to handle kernel paging request at 00000000757d4900
>>>> IP: [<ffffffff810b59af>] cpuacct_charge+0x5f/0xa0
>>>> PGD 0
>>>> Thread overran stack, or stack corrupted
>>>
>>> Hmmmm. That is not at all informative, especially as it's only
>>> dumped the interrupt stack and not the stack or the task that it
>>> has detected as overrun or corrupted.
>>>
>>> Can you turn on all the stack overrun debug options? Maybe even
>>> turn on the stack tracer to get an idea of whether we are recursing
>>> deeply somewhere we shouldn't be?
>>
>> Digging around under "Kernel hacking".... I already have
>> DEBUG_STACK_USAGE, DEBUG_STACKOVERFLOW, and STACK_TRACER, and I can try
>> turning on the latter. (Will I be able to get information out of it
>> before the panic?)
>
> just keep taking samples of the worst case stack usage as the test
> runs. If there's anything unusual before the failure then it will
> show up, otherwise I'm not sure how to track this down...

I think it should print "maximum stack depth" messages whenever a stack
reaches a new max excursion...

> Cheers,
>
> Dave.