Date: Thu, 19 Mar 2015 14:47:14 -0400
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>, Eric Sandeen <sandeen@sandeen.net>,
        linux-nfs@vger.kernel.org, xfs@oss.sgi.com
Subject: Re: panic on 4.20 server exporting xfs filesystem
Message-ID: <20150319184714.GB20852@fieldses.org>
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On Thu, Mar 19, 2015 at 06:27:31PM +0100, Christoph Hellwig wrote:
> FYI, I've now managed to reproduce the issue.  I haven't had time
> to dig deeper, but it smells a lot like a callback path issue.
> 
> Can you send the recursion fix to Linus ASAP and I'll send you a patch
> to turn the nopnfs option into a pnfs one, so we're at least doing
> fine for 4.0 in any case.

Sure, sounds good.

Also, there's the problem that when this is turned on a client can end
up doing unnecessary LAYOUTGET.  Do we have a plan for that?

Possibilities:

	- Just depend on export flags: but some clients may have direct
	  access and some not.  If the clients with direct access or all
	  easily identifiable by IP subnet, maybe it's not a big deal.
	  Still, seems like an administrative hassle.

	- Do nothing, assume the client can deal with this with some
	  kind of heuristics, and/or that the GETLAYOUT calls can be
	  made very cheap.  Not sure if that's true.

	- Use something like GETDEVLICELIST so the client can figure out
	  in one go whether any layouts on a given filesystem will work.
	  I forget what the problems with GETDEVICELIST were.

> I hope to debug this and may even have
> a real fix soon, but so far I don't know how long it will take.

OK, thanks.

--b.