Re: Massive NFS problems on large cluster with large number of mounts

Jeff Layton
2008-07-29T11:32:45Z

On Mon, 28 Jul 2008 16:55:50 -0400
"Chuck Lever" <chuck.lever@oracle.com> wrote:

> On Thu, Jul 17, 2008 at 11:11 AM, Chuck Lever <chuck.lever@oracle.com> wrote:
> > On Thu, Jul 17, 2008 at 10:48 AM, J. Bruce Fields <bfields@fieldses.org> wrote:
> >> On Thu, Jul 17, 2008 at 10:47:25AM -0400, Chuck Lever wrote:
> >>> On Wed, Jul 16, 2008 at 3:06 PM, J. Bruce Fields <bfields@fieldses.org> wrote:
> >>> > The immediate problem seems like a kernel bug to me--it seems to me that
> >>> > the calls to local daemons should be ignoring {min_,max}_resvport. (Or
> >>> > is there some way the daemons can still know that those calls come from
> >>> > the local kernel?)
> >>>
> >>> I tend to agree. The rpcbind client (at least) does specifically
> >>> require a privileged port, so a large min/max port range would be out
> >>> of the question for those rpc_clients.
> >>
> >> Any chance I could talk you into doing a patch for that?
> >
> > I can look at it when I get back next week.
>
> I've been pondering this.
>
> It seems like the NFS client is a rather unique case for using
> unprivileged ports; most or all of the other RPC clients in the kernel
> want to use privileged ports pretty much all the time, and have
> learned to switch this off as needed and appropriate. We even have an
> internal API feature for doing this: the RPC_CLNT_CREATE_NONPRIVPORT
> flag to rpc_create().
>
> And instead of allowing a wide source port range, it would be better
> for the NFS client to use either privileged ports, or unprivileged
> ports, but not both, for the same mount point. Otherwise we could be
> opening ourselves up for non-deterministic behavior: "How come
> sometimes I get EPERM when I try to mount my NFS servers, but other
> times the same mount command works fine?" or "Sometimes after a long
> idle period my NFS mount points stop working, and all the programs
> running on the mount point get EACCES."
>
> It seems like a good solution would be to:
>
> 1. Make the xprt_minresvport and xprt_maxresvport sysctls mean what
> they say: they are _reserved_ port limits. Thus xprt_maxresvport
> should never be allowed to be larger than 1023, and xprt_minresvport
> should always be made to be strictly less than xprt_maxresvport; and
>
> 2. Introduce a mechanism to specifically enable the NFS client to use
> non-privileged ports. It could be a new mount option like "insecure"
> (which is what some other O/Ses use) or "unpriv-source-port" for
> example. I tend to dislike the former because such a feature is
> likely to be quite useful with Kerberos-authenticated NFS, and
> "sec=krb5,insecure" is probably a little funny looking, but
> "sec=krb5,unpriv-source-port" makes it pretty clear what is going on.
>
> Such an "insecure" mount option would then set
> RPC_CLNT_CREATE_NONPRIVPORT on rpc_clnt's created on behalf of the NFS
> client.
>
> I'm not married to the names of the options, or even using a mount
> option at all (although that seems like a natural place to put such a
> feature).
>
> Thoughts?
>

IMNSHO, the whole concept of "privileged ports" is pretty antiquated
anyway. It doesn't mean much unless you have a very tightly controlled
physical network...

Being able to allow the client to use non-privileged ports could be
useful. It's less of a problem than it used to be since the NFS client
shares sockets better now, but it could still be a problem in an HPC-type
environment. The NFS server already has an option to allow for clients
that do this so we might as well allow the client to do it too.

I tend to be of the opinion that we should try to use option names that
other OS's have already established where possible. This makes it easier
for admins in mixed environments (shared autofs maps and fewer option
synonyms to remember). My vote would be for calling the new option
"insecure", or at least making "insecure" a synonym for whatever the
new mount option is.

--
Jeff Layton <jlayton@redhat.com>