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

Chuck Lever
2008-07-28T20:55:52Z

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?

--
Chuck Lever