linux-kernel - Re: [NFS] blocks of zeros (NULLs) in NFS files in kernels >= 2.6.20

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Date:	Fri, 5 Sep 2008 15:14:35 -0700
From:	Aaron Straus <aaron@...finllc.com>
To:	Chuck Lever <chuck.lever@...cle.com>
Cc:	Neil Brown <neilb@...e.de>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	LKML Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [NFS] blocks of zeros (NULLs) in NFS files in kernels >= 2.6.20

Hi,

On Sep 05 04:36 PM, Chuck Lever wrote:
> I have the latest Fedora 9 kernels on two clients, mounting via NFSv3  
> using "actimeo=600" (for other reasons).  The server is OpenSolaris  
> 2008.5.
> 
> reader.py reported zeroes in the test file after about 5 minutes.

Awesome.  Thanks for testing!  Our actime is much shorter which is
probably why it happens sooner for us.

> Looking at the file a little later, I don't see any problems with it.
> 
> Since your scripts are not using any kind of serialization (ie file  
> locking) between the clients, I wonder if non-determinant behavior is  
> to be expected.

Hmm... yep.  I don't know what guarantees we want to make.   The
behavior doesn't seem to be consistent with older kernels though... so
I'm thinking it might be a bug.

We hit this particular issue because we have scripts which essentially
'tail -f' log files looking for errors.   They miss log messages (and
see corrupted ones) b/c of the NULLs.  That's also why there is no
serialization.... we don't need it when grep'ing through log messages.

I'm bisecting now.  I see a block of intricate-looking NFS patches, I'll
try to narrow it down to a particular commit.  

I'll also get the wireshark data at that point.

					Thanks,
					=a=

-- 
===================
Aaron Straus
aaron@...finllc.com

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