kern/131342: [nfs] mounting/unmounting of disks causes NFS to fail

[Rick Macklem]

Martin Birgmeier wrote:
> The following reply was made to PR kern/131342; it has been noted by
> GNATS.
> 
> From: Martin Birgmeier <Martin.Birgmeier at aon.at>
> To: bug-followup at FreeBSD.org
> Cc:
> Subject: Re: kern/131342: [nfs] mounting/unmounting of disks causes
> NFS to
> fail
> Date: Fri, 08 Jul 2011 15:00:03 +0200
> 
> This is a friendly reminder that some kind soul with knowledge of the
> relevant kernel parts look into this... the error can easily be
> reproduced. I just had it on a 7.4 system which did heavy reading from
> an 8.2 server. When I mounted something on the server, the client got
> a
> "Permission denied" reply.
> 
> So, to recap the scenario:
> 
> 7.4 NFS client
> 8.2 NFS server
> client mounts a fs from the server (via IPv4, might be interesting to
> look at http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/151681, too,
> but
> that is unrelated)
> client does heavy i/o on the mounted fs
> server does a mount (on its side, in this case it was from an md
> device)
> 
> --> error: client gets back some NFS error (in this case "permission
> denied")
> 
Oh, and one more question...
Is the error persistent (ie. is the client mount unusable until remounted)
or does the mount point work after the mount/unmount of the other volume
has completed?

If it just happens when the other volume is unmounted/mounted, make sure
that you aren't using the "soft" option for your client mounts. ("soft"
implies that an RPC fails after a timeout, and an unmount/mount of
another volume could delay the RPC for a while, until the mount list
is unlocked.)

rick