Re: NFS Caching broken in 4.19.37

[Anton Ivanov]

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@xxxxxxxxxxxxxxxxxx> 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/