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Date:   Fri, 8 Jan 2021 16:49:53 +0100
From:   Kurt Garloff <>
To:     Trond Myklebust <>,
        "" <>,
        "" <>
Cc:     "" <>
Subject: Re: NFS 4.2 client support broken on 5.10.5

Hi Trond,

Am 08.01.21 um 15:39 schrieb Kurt Garloff:
> Hi Trond,
> On 08/01/2021 12:58, Trond Myklebust wrote:
>> On Fri, 2021-01-08 at 12:41 +0100, Kurt Garloff wrote:
>>> [...]
>>> The kernel tree is on an NFS share, and I run 5.10.5 client kernel
>>> against the kernel NFS (4.2) server, running a 5.10.3 kernel.
>>> The issue does NOT occur on a 5.10.3 client kernel, but is easily
>>> reproducible on 5.10.5. Note that 5.10.5 on a local file system or
>>> against an NFSv3 server does not show the issue.
>>> Test program that reproduces this on the first pwrite64() is
>>> attached.
>>> Note that the call to ftruncate() is required to make the problem
>>> happen.
>>> I could go on bisecting this to a particular patch, but you'll
>>> probably be able to see right away what's wrong.
>> Hmm... If this is NFSv4.2 do you have READ_PLUS turned on or off in
>> .config? It really is not safe to enable READ_PLUS on 5.10 kernels
>> since that can cause random memory corruption.
> OK, it is turned on in my kernel -- looks like I have not read the
> warning in the config option help text carefully enough ...
> I'll test what happens if I switch it off and report back.

OK, I compiled a kernel without support for READ_PLUS
and the test program magically succeeds.

So take my report as input to the developers that work
on making READ_PLUS work. Maybe they want to add
my little program to their CI suite.


Kurt Garloff <>, Cologne, Germany

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