Re: NFSD automatically releases all states when underlying file system is unmounted

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2025-03-21 at 10:36 -0400, Benjamin Coddington wrote:
> On 20 Mar 2025, at 13:53, Chuck Lever wrote:
> 
> > On 3/19/25 5:46 PM, NeilBrown wrote:
> > > On Thu, 20 Mar 2025, Dai Ngo wrote:
> > > > Hi,
> > > > 
> > > > Currently when the local file system needs to be unmounted for maintenance
> > > > the admin needs to make sure all the NFS clients have stopped using any files
> > > > on the NFS shares before the umount(8) can succeed.
> > > 
> > > This is easily achieved with
> > >   echo /path/to/filesystem > /proc/fs/nfsd/unlock_filesystem
> > > 
> > > Do this after unexporting and before unmounting.
> > 
> > Seems like administrators would expect that a filesystem can be
> > unmounted immediately after unexporting it. Should "exportfs" be changed
> > to handle this extra step under the covers? Doesn't seem like it would
> > be hard to do, and I can't think of a use case where it would be
> > harmful.
> 
> No. I think that admins don't expect to lose all their NFS client's state if
> they're managing the exports.  That would be a really big and invisible change
> to existing behavior.
> 

If we're unexporting the filesystem though, then ISTM like we ought to
cancel any state that was held on it. Are you concerned the admin
inadvertently unexporting something or is there another use-case you're
worried about?

-- 
Jeff Layton <jlayton@kernel.org>