Re: NFS Force Unmounting

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Nov 08, 2017 at 07:08:25AM -0500, Jeff Layton wrote:
> On Wed, 2017-11-08 at 14:30 +1100, NeilBrown wrote:
> > What to people think of the following as an approach
> > to Joshua's need?
> > 
> > It isn't complete by itself: it needs a couple of changes to
> > nfs-utils so that it doesn't stat the mountpoint on remount,
> > and it might need another kernel change so that the "mount" system
> > call performs the same sort of careful lookup for remount as  the umount
> > system call does, but those are relatively small details.
> > 
> 
> Yeah, that'd be good.
> 
> > This is the patch that you will either love of hate.
> > 
> > With this patch, Joshua (or any other sysadmin) could:
> > 
> >   mount -o remount,retrans=0,timeo=1 /path
> > 
> > and then new requests on any mountpoint from that server will timeout
> > quickly.
> > Then
> >   umount -f /path
> >   umount -f /path
...
> Looks like a reasonable approach overall to preventing new RPCs from
> being dispatched once the "force" umount runs.

I've lost track of the discussion--after this patch, how close are we to
a guaranteed force unmount?  I assume there are still a few obstacles.

> I do wonder if this ought to be more automatic when you specify -f on
> the umount. Having to manually do a remount first doesn't seem very
> admin-friendly.

It's an odd interface.  Maybe we could wrap it in something more
intuitive.

I'd be nervous about making "umount -f" do it.  I think administrators
could be unpleasantly surprised in some cases if an "umount -f" affects
other mounts of the same server.

--b.