Re: NFS Caching broken in 4.19.37

[Anton Ivanov]

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.

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
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https://www.cambridgegreys.com/