Re: fscache/NFS re-export server lockup

Daire Byrne
2025-12-19T17:02:01Z

On Fri, 19 Dec 2025 at 16:25, Mike Owen <mjnowen@gmail.com> wrote:
>
> We are using NFS re-exporting with fscache but have had a number of
> lockups with re-export servers.
>
> The NFS re-export servers are running Ubuntu 24.04 with a
> 6.14.0-36-generic kernel mounting Isilon and NetApp filers over NFSv3.
>
> The NFS clients are mounting the re-exported shares over NFSv4 and
> running AlmaLinux 9.6.
>
> When the re-export server locks up, it is not possible to access the
> /var/cache/fscache directory (separate file system) on the server and
> all clients are hanging on their mounts from the re-export.

That does kind of point to a filesystem problem with /var/cache/fscache itself?

Can you stop the nfs server and is access to /var/cache/fscache still blocked?

> When the server is rebooted, most of the contents of the
> /var/cache/fscache directory is missing e.g. the file system contents
> before the lockup may have been a few TBs, but after a reboot only a
> few hundred GBs.

I can't say I've ever seen that before... we use ext4 for the fscache
filesystem mount on /var/cache/fscache.

And I presume there is definitely nothing else that might be
interacting with that /var/cache/fscache filesystem outside of fscache
or cachefilesd?

Our /etc/cachefilesd.conf is pretty basic (brun 30%, bcull 10%, bstop 3%).

> The kern.log (below) from the re-export server reports the following
> when the lockup happens.
>
> We have tried using a more recent 6.17.11 kernel on the re-export
> server and changing the fscache file system from ext4 to xfs, but
> still have the same lockups.

We were running a heavily patched v6.4 kernel for almost 2 years and
have just updated to v6.18.1 with no patches - so far so good!

We are mostly re-exporting NFSv3 -> NFSv3 (Linux NFS storage servers)
with a small amount of NFSv3 -> NFSv4.2 (Netapps).

> Any ideas on what is happening here - and how it may be fixed?

Sorry I can't be more helpful.

Daire