Re: NFS Caching broken in 4.19.37

[Anton Ivanov <anton.ivanov@cambridgegreys.com>]

On 21/02/2021 09:13, Salvatore Bonaccorso wrote:
> Hi,
> 
> On Sat, Feb 20, 2021 at 08:16:26PM +0000, Chuck Lever wrote:
>>
>>
>>> On Feb 20, 2021, at 3:13 PM, Anton Ivanov <anton.ivanov@cambridgegreys.com> wrote:
>>>
>>> On 20/02/2021 20:04, Salvatore Bonaccorso wrote:
>>>> Hi,
>>>>
>>>> On Mon, Jul 08, 2019 at 07:19:54PM +0100, Anton Ivanov wrote:
>>>>> Hi list,
>>>>>
>>>>> NFS caching appears broken in 4.19.37.
>>>>>
>>>>> The more cores/threads the easier to reproduce. Tested with identical
>>>>> results on Ryzen 1600 and 1600X.
>>>>>
>>>>> 1. Mount an openwrt build tree over NFS v4
>>>>> 2. Run make -j `cat /proc/cpuinfo | grep vendor | wc -l` ; make clean in a
>>>>> loop
>>>>> 3. Result after 3-4 iterations:
>>>>>
>>>>> State on the client
>>>>>
>>>>> ls -laF /var/autofs/local/src/openwrt/build_dir/target-mips_24kc_musl/linux-ar71xx_tiny/linux-4.14.125/arch/mips/include/generated/uapi/asm
>>>>>
>>>>> total 8
>>>>> drwxr-xr-x 2 anivanov anivanov 4096 Jul  8 11:40 ./
>>>>> drwxr-xr-x 3 anivanov anivanov 4096 Jul  8 11:40 ../
>>>>>
>>>>> State as seen on the server (mounted via nfs from localhost):
>>>>>
>>>>> ls -laF /var/autofs/local/src/openwrt/build_dir/target-mips_24kc_musl/linux-ar71xx_tiny/linux-4.14.125/arch/mips/include/generated/uapi/asm
>>>>> total 12
>>>>> drwxr-xr-x 2 anivanov anivanov 4096 Jul  8 11:40 ./
>>>>> drwxr-xr-x 3 anivanov anivanov 4096 Jul  8 11:40 ../
>>>>> -rw-r--r-- 1 anivanov anivanov   32 Jul  8 11:40 ipcbuf.h
>>>>>
>>>>> Actual state on the filesystem:
>>>>>
>>>>> ls -laF /exports/work/src/openwrt/build_dir/target-mips_24kc_musl/linux-ar71xx_tiny/linux-4.14.125/arch/mips/include/generated/uapi/asm
>>>>> total 12
>>>>> drwxr-xr-x 2 anivanov anivanov 4096 Jul  8 11:40 ./
>>>>> drwxr-xr-x 3 anivanov anivanov 4096 Jul  8 11:40 ../
>>>>> -rw-r--r-- 1 anivanov anivanov   32 Jul  8 11:40 ipcbuf.h
>>>>>
>>>>> So the client has quite clearly lost the plot. Telling it to drop caches and
>>>>> re-reading the directory shows the file present.
>>>>>
>>>>> It is possible to reproduce this using a linux kernel tree too, just takes
>>>>> much more iterations - 10+ at least.
>>>>>
>>>>> Both client and server run 4.19.37 from Debian buster. This is filed as
>>>>> debian bug 931500. I originally thought it to be autofs related, but IMHO it
>>>>> is actually something fundamentally broken in nfs caching resulting in cache
>>>>> corruption.
>>>> According to the reporter downstream in Debian, at
>>>> https://bugs.debian.org/940821#26 thi seem still reproducible with
>>>> more recent kernels than the initial reported. Is there anything Anton
>>>> can provide to try to track down the issue?
>>>>
>>>> Anton, can you reproduce with current stable series?
>>>
>>> 100% reproducible with any kernel from 4.9 to 5.4, stable or backports. It may exist in earlier versions, but I do not have a machine with anything before 4.9 to test at present.
>>
>> Confirming you are varying client-side kernels. Should the Linux
>> NFS client maintainers be Cc'd?
> 
> Ok, agreed. Let's add them as well. NFS client maintainers any ideas
> on how to trackle this?

This is not observed with Debian backports 5.10 package

uname -a
Linux madding 5.10.0-0.bpo.3-amd64 #1 SMP Debian 5.10.13-1~bpo10+1 
(2021-02-11) x86_64 GNU/Linux

I left the testcase running for ~ 4 hours on a 6core/12thread Ryzen. It 
should have blown up 10 times by now.

So one of the commits between 5.4 and 5.10.13 fixed it.

If nobody can think of a particular commit which fixes it, I can try 
dissecting it during the week.

A.

> 
>>
>>>  From 1-2 make clean && make  cycles to one afternoon depending on the number of machine cores. More cores/threads the faster it does it.
>>>
>>> I tried playing with protocol minor versions, caching options, etc - it is still reproducible for any nfs4 settings as long as there is client side caching of metadata.
>>>
>>> A.
>>>
>>>>
>>>> Regards,
>>>> Salvatore
>>>>
>>>
>>> -- 
>>> Anton R. Ivanov
>>> Cambridgegreys Limited. Registered in England. Company Number 10273661
>>> https://www.cambridgegreys.com/
>>
>> --
>> Chuck Lever
> 
> Regards,
> Salvatore
> 


-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/