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Re: panic on 4.20 server exporting xfs filesystem

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: panic on 4.20 server exporting xfs filesystem
From: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
Date: Wed, 4 Mar 2015 17:27:09 -0500
Cc: Christoph Hellwig <hch@xxxxxx>, linux-nfs@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20150304220900.GX18360@dastard>
References: <20150303221033.GB19439@xxxxxxxxxxxx> <20150303224456.GV4251@dastard> <20150304020826.GD19439@xxxxxxxxxxxx> <20150304155421.GE1627@xxxxxxxxxxxx> <20150304220900.GX18360@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
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?)

I guess I'll also try SCHED_STACK_END_CHECK.  Anything else I'm missing?

--b.

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