On Thu, 2011-08-04 at 12:49 -0400, J. Bruce Fields wrote:
> On Thu, Aug 04, 2011 at 06:43:13PM +0200, Frank van Maarseveen wrote:
> > On Thu, Aug 04, 2011 at 12:34:52PM -0400, J. Bruce Fields wrote:
> > > On Thu, Aug 04, 2011 at 12:30:19PM +0200, Frank van Maarseveen wrote:
> > > > Both client- and server run 2.6.39.3, NFSv3 over UDP (without the
> > > > relock_filesystem patch proposed earlier).
> > > >
> > > > A second client has an exclusive lock on a file on the server. The
> > > > client under test calls fcntl(F_SETLKW) to wait for the same exclusive
> > > > lock. Wireshark sees NLM V4 LOCK calls resulting in NLM_BLOCKED.
> > > >
> > > > Next the server is rebooted. The second client recovers the lock
> > > > correctly. The client under test now receives NLM_DENIED_GRACE_PERIOD for
> > > > every NLM V4 LOCK request resulting from the waiting fcntl(F_SETLKW). When
> > > > this changes to NLM_BLOCKED after grace period expiration the fcntl
> > > > returns -ENOLCK ("No locks available.") instead of continuing to wait.
> > >
> > > So that sounds like a client bug, and correct behavior from the server
> > > (assuming the second client was still holding the lock throughout).
> >
> > yes.
Is the client actually asking for a blocking lock after the grace period
expires?
> > >
> > > > server:/proc/locks shows two entries for the file after the -ENOLCK. When
> > > > the second client gives up its lock because the program running there
> > > > is killed one entry in server:/proc/locks remains indefinately: as a
> > > > result no NFS client can lock the file anymore.
> > >
> > > But that sounds like a server bug--what do the two entries look like?
> >
> > I think the server assumes correct client behavior; the client under
> > test resulted in a '->' prefixed entry. The fcntl at the client just
> > shouldn't have returned yet.
>
> Oh, right, so did you see a granted callback returned to the client?
The client will reject any unsolicited GRANTED callbacks with an
NLM_LCK_DENIED. As far as I can see, nlmsvc_grant_reply() then only
removes the block, it doesn't cancel the lock...
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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