Re: panic on 4.20 server exporting xfs filesystem

[Dave Chinner <david@fromorbit.com>]

On Wed, Mar 04, 2015 at 04:49:09PM -0600, Eric Sandeen wrote:
> 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...

That gets printed only when the process exits, IIRC.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com