Un-unmountable NFS mountpoints with "Stale NFS file handle" - is this normal behavior?

Un-unmountable NFS mountpoints with "Stale NFS file handle" - is this normal behavior?

[Karsten Hohmeier]

Dear NFS list members,

I recently contacted a few active NFS devs with an issue i ran into:

We run a XenServer 6.5 (Kernel 3.10) with an older version of nfs-utils
(1.0.9). NFS mountpoints on that machine acting as a client can not be
unmounted (not even forcibly or lazy) after the connection to the NFS
server broke for some reason.

Most commands fail with "Stale NFS file handle".

The Internet tells me this situation is unfixable and requires a reboot
of the client to resolve. This is a pretty bad solution on a heavily
loaded virtualization host.

The response of Bruce Fields was: "Sounds like normal behavior, ..."
(Sorry for not posting to the list in the first place, btw.)

I'm still looking for some explanation why this happens, how it can be
considered "normal behavior" and if it can be fixed/avoided/mitigated
without rebooting.

Best regards

Karsten Hohmeier

Re: Un-unmountable NFS mountpoints with "Stale NFS file handle" - is this normal behavior?

[NeilBrown]

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On Sun, Aug 21 2016, Karsten Hohmeier wrote:

> Dear NFS list members,
>
> I recently contacted a few active NFS devs with an issue i ran into:
>
> We run a XenServer 6.5 (Kernel 3.10) with an older version of nfs-utils
> (1.0.9). NFS mountpoints on that machine acting as a client can not be
> unmounted (not even forcibly or lazy) after the connection to the NFS
> server broke for some reason.
>
> Most commands fail with "Stale NFS file handle".
>
> The Internet tells me this situation is unfixable and requires a reboot
> of the client to resolve. This is a pretty bad solution on a heavily
> loaded virtualization host.
>
> The response of Bruce Fields was: "Sounds like normal behavior, ..."
> (Sorry for not posting to the list in the first place, btw.)
>
> I'm still looking for some explanation why this happens, how it can be
> considered "normal behavior" and if it can be fixed/avoided/mitigated
> without rebooting.

This was fixed 3 years ago in Linux 3.12

Commit: 8033426e6bdb ("vfs: allow umount to handle mountpoints without revalidating them")

(and probably a few other related patches).

You need to be sure you have a version of util-linux where "umount -f"
and "umount -l" don't stat() the mount point.

NeilBrown

>
> Best regards
>
> Karsten Hohmeier
>
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Re: Un-unmountable NFS mountpoints with "Stale NFS file handle" - is this normal behavior?

[Karsten Hohmeier]

Thanks for the helpful answer!

> This was fixed 3 years ago in Linux 3.12

I guess it is time to update that machine then ...

> 
> Commit: 8033426e6bdb ("vfs: allow umount to handle mountpoints without revalidating them")
> 
> (and probably a few other related patches).
> 
> You need to be sure you have a version of util-linux where "umount -f"
> and "umount -l" don't stat() the mount point.
> 
> NeilBrown

In dev. time terms digging this up is pretty much archeology.

Best regards

Karsten Hohmeier