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Re: [Linux-cluster] GFS2 + NFS crash BUG: Unable to handle kernel NULL pointer deference



On Mon, Jul 11, 2011 at 11:43:58AM +0100, Steven Whitehouse wrote:
> Hi,
> 
> On Mon, 2011-07-11 at 09:30 +0100, Alan Brown wrote:
> > On 08/07/11 22:09, J. Bruce Fields wrote:
> > 
> > > With default mount options, the linux NFS client (like most NFS clients)
> > > assumes that a file has a most one writer at a time.  (Applications that
> > > need to do write-sharing over NFS need to use file locking.)
> > 
> > The problem is that file locking on V3 isn't passed back down to the 
> > filesystem - hence the issues with nfs vs samba (or local disk 
> > access(*)) on the same server.

The NFS server *does* acquire locks on the exported filesystem (and does
it the same way for v2, v3, and v4).

For local filesystems (ext3, xfs, btrfs), this is sufficient.

For exports of cluster filesystems like gfs2, there are more complicated
problems that, as Steve says, will require some work to do to fix.

Samba is a more complicated issue due to the imperfect match between
Windows and Linux locking semantics, but depending on how it's
configured Samba will also acquire locks on the exported filesystem.

--b.


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