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

[Colin Simpson]

OK, so my question is, is there any other reason apart from the risk of
individual file corruption from locking being incompatible between
local/samba vs NFS that may lead to issues i.e. we aren't really
interested in locking working between NFS and local/samba access just
that it works consistently in NFS when accessing files that way (with a
single node server) and locally/samba when accessing files that way.

I mean I'm thinking of, for example, I have a build that generates
source code via NFS then some time later a PC comes in via Samba and
accesses these files for building on that environment. The two systems
aren't requiring locking to work cross platform/protocol, just need to
be exported to the two systems. But locking on each one separately is
useful. 

If there are and we should be using all access via NFS on NFS exported
filesystems, one issue that also springs to mind is commercial backup
systems that support GFS2 but don't support backing up via NFS.

Is there anything else I should know about GFS2 limitations?
Is there a book "GFS: The Missing Manual"? :)

Thanks

Colin

On Mon, 2011-07-11 at 13:05 +0100, J. Bruce Fields wrote:
> 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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> 

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