[Linux-cluster] RHEL/CentOS-6 HA NFS Configuration Question

[Benjamin Coddington]

Those running HA NFS should be aware of the following two NFSD open leaks.

The first is the nfs4_open_downgrade leak:
http://marc.info/?l=linux-nfs&m=131077202109185&w=2
https://bugzilla.redhat.com/show_bug.cgi?id=714153

Redhat supposedly fixed this, but I never saw the errata go by.. while we
waited for them to fix it, we went to an upstream kernel and got bit
by this one:

http://marc.info/?l=linux-nfs&m=131077202109185&w=2

NFSD open leaks will cause your filesystems to fail to umount, even after
waiting through your lease time.  You'll see the device's open count
will be non-zero (dmsetup info <device>), even though the filesystem
is unexported, and kernel nfsds are stopped.

We've been running our NFS4 HA cluster for a few months now on
a 3.2.5 kernel, and failover/recovery works well.

Ben

On May 16, 2012, at 2:19 PM, Colin Simpson wrote:

> This is interesting.
> 
> We very often see the filesystems fail to umount on busy clustered NFS
> servers.
> 
> What is the nature of the "real fix"?
> 
> I like the idea of NFSD fully being in user space, so killing it would
> definitely free the fs.
> 
> Alan Brown (who's on this list) recently posted to a RH BZ that he was
> one of the people who moved it into kernel space for performance reasons
> in the past (that are no longer relevant):
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=580863#c9
> 
> , but I doubt this is the fix you have in mind.
> 
> Colin
> 
> On Tue, 2012-05-15 at 20:21 +0200, Fabio M. Di Nitto wrote:
>> This solves different issues at startup, relocation and recovery
>> 
>> Also note that there is known limitation in nfsd (both rhel5/6) that
>> could cause some problems in some conditions in your current
>> configuration. A permanent fix is being worked on atm.
>> 
>> Without extreme details, you might have 2 of those services running on
>> the same node and attempting to relocate one of them can fail because
>> the fs cannot be unmounted. This is due to nfsd holding a lock (at
>> kernel level) to the FS. Changing config to the suggested one, mask the
>> problem pretty well, but more testing for a real fix is in progress.
>> 
>> Fabio
>> 
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