Breaking locks on a lame server?

[Erik Walthinsen <omega@temple-baptist.com>]

We've got a configuration with a NAS machine (3ware SATA RAID) running a 
2.4.26 kernel is in use by a number of client machines, each running 
multiple instances of user-mode-linux.  Most all "block devices" presented 
to the UML instances are located on the NAS, exported via NFS.  The clients 
are currently a mix of 2.4.26 and 2.6.15.6.

The problem is, whenever there's any kind of abnormal shutdown of either a 
UML instance or the machine that's running it, a NFS lock is left in place. 
  This means that UML refuses to start up again using those files, unless I 
patch the UML kernel to avoid F_SETLK, which is of course very unsafe (two 
UMLs touching the same file means EDEADFILE).

I've seen other suggestions for breaking locks that involve restarting statd 
on the clients, etc., but the problem is this: these locks are persistent 
across reboots of the clients.  IIRC they're also persistent *between* 
clients, so I can't start a UML instance on an alternate machine either.

We're planning an upgrade of the NAS box to 2.6 as soon as we can, but that 
means a system-wide shutdown of all our customer's UML instances, which 
isn't something we do lightly.

1) am I to expect 2.6's NFS server implementation to somehow solve this?
2) if not, and in the meantime, are there any means by which I can inspect 
(lslk does nothing) and hopefully kill these locks?

(I'm not on the list, already on too many, so please make sure to send to: 
or cc: me)

Thankx,
       Omega
       aka Erik Walthinsen
       omega@vcolo.com


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