Re: NFS Caching broken in 4.19.37

[Salvatore Bonaccorso <carnil@debian.org>]

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?

> 
> > 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