Re: NFS Caching broken in 4.19.37

[Chuck Lever <chuck.lever@oracle.com>]

> 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?


> 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