Re: [PATCH 3/8] mountd: remove 'dev_missing' checks

[NeilBrown <neilb@suse.com>]

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On Thu, Aug 18 2016, Chuck Lever wrote:

>> On Aug 17, 2016, at 9:32 PM, NeilBrown <neilb@suse.com> wrote:
>> 
>> On Wed, Aug 17 2016, J. Bruce Fields wrote:
>>>> 
>>>> 
>>>> There is another issue related to this that I've been meaning to
>>>> mention.  It related to the start-up ordering rather than shut down.
>>>> 
>>>> When you try to mount an NFS filesystem and the server isn't responding,
>>>> mount.nfs retries for a little while and then - if "bg" is given - it
>>>> forks and retries a bit longer.
>>>> While it keeps gets failures that appear temporary, like ECONNREFUSED or
>>>> ETIMEDOUT (see nfs_is_permanent_error()) it keeps retrying.
>>>> 
>>>> There is typically a window between when rpcbind starts responding to
>>>> queries, and when nfsd has registered with it.  If mount.nfs sends an
>>>> rpcbind query in this window. It gets RPC_PROGNOTREGISTERED which
>>>> nfs_rewrite_pmap_mount_options maps to EOPNOTSUPP, and
>>>> nfs_is_permanent_error() thinks that is a permanent error.
>>> 
>>> Looking at rpcbind(8)....  Shouldn't "-w" prevent this by loading some
>>> registrations before it starts responding to requests?
>> 
>> "-w" (which isn't listed in the SYNOPSIS!) only applies to a warm-start
>> where the daemons which previously registered are still running.
>> The problem case is that the daemons haven't registered yet (so we don't
>> necessarily know what port number they will get).
>> 
>> To address the issue in rpcbind, we would need a flag to say "don't
>> respond to lookup requests, just accept registrations", then when all
>> registrations are complete, send some message to rpcbind to say "OK,
>> respond to lookups now".  That could even be done by killing and
>> restarting with "-w", though that it a bit ugly.
>
> An alternative would be to create a temporary firewall rule that
> blocked port 111 to remote connections. Once local RPC services
> had registered, the rule is removed.
>
> Just a thought.

Interesting ..... probably the sort of thing that I would resort to if I
really needed to fix this and didn't have any source code.
But fiddling with fire-wall rules is not one of my favourite things so I
think I stick with a more focussed solution.
Thanks!

NeilBrown


>
>
>> I'm leaning towards having mount retry after RPC_PROGNOTREGISTERED for
>> fg like it does with bg.
>
> It probably should do that. If rpcbind is up, then the other
> services are probably on their way.
>
>
> --
> Chuck Lever

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