Re: NFS hang + umount -f: better behaviour requested.

[Robin Lee Powell <rlpowell@digitalkingdom.org>]

On Tue, Aug 21, 2007 at 09:27:06AM +1000, Neil Brown wrote:
> On Monday August 20, rlpowell@digitalkingdom.org wrote:
> > (cc's to me appreciated)
> > 
> > It would be really, really nice if "umount -f" against a hung
> > NFS mount actually worked on Linux.  As much as I hate Solaris,
> > I consider it the gold standard in this case: If I say "umount
> > -f /mount/that/is/hung" it just goes away, immediately, and
> > anything still trying to use it dies (with EIO, I'm told).
> 
> Have you tried "umount -l"?   How far is that from your
> requirements?

I actually talked about that further down.  The short version: quite
far.

The long version:

It leaves a bunch of hung processes, with no real way for me to
determine which processes are hung on the now-non-existent mount,
and (at least with autofs) it leaves /etc/mtab in an inconsistent
state, so I had to edit it to restart autofs.  Only a mild
improvement on rebooting, says I.

Also, it took a really long time (minutes) to return.

> Alternately:
>    mount --move /problem/path /somewhere/else
>    umount -f /somewhere/else
>    umount -l /somewhere/else
> 
> might be a little closer to what you want.

I don't think that would solve the problem: the umount -f would
still hang and eventually return busy, fuser would still hang, and
umount -l would still leave inconsistent crap lying around.

> Though I agree that it would be nice if we could convince all
> subsequent requests to a server to fail EIO instead of just the
> currently active ones.  I'm not sure that just changing "umount
> -f" is the right interface though....  Maybe if all the server
> handles appeared in sysfs and have an attribute which you could
> set to cause all requests to fail...

I have no opinion on interface details, I simply know that on
Solaris, "umount -f" Just Works, and I would love to have similar
behaviour on Linux.

-Robin

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