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Subject: Re: NFS 4.2 client support broken on 5.10.5
From:   Kurt Garloff <kurt@garloff.de>
To:     Trond Myklebust <trondmy@hammerspace.com>,
        "NeilB@suse.de" <NeilB@suse.de>,
        "Anna.Schumaker@Netapp.com" <Anna.Schumaker@Netapp.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <ee320885-9a78-80b8-9341-7c631df60d3a@garloff.de>
 <2f401e0a738b7acb926bd2375012e6384a2cd9b6.camel@hammerspace.com>
 <927fcf61-7992-1b9f-ae39-c71d96323fbc@garloff.de>
Message-ID: <85cd2357-b835-c8b4-ef98-e6b486abbbdc@garloff.de>
Date:   Fri, 8 Jan 2021 16:49:53 +0100
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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.

Thanks,

-- 
Kurt Garloff <kurt@garloff.de>, Cologne, Germany