[PATCH] NFSv4: fix a mount deadlock in NFS v4.1 client

[Oleksandr Tymoshenko <ovt@google.com>]

>> nfs41_init_clientid does not signal a failure condition from
>> nfs4_proc_exchange_id and nfs4_proc_create_session to a client which
>> may
>> lead to mount syscall indefinitely blocked in the following stack

> NACK. This will break all sorts of recovery scenarios, because it
> doesn't distinguish between an initial 'mount' and a server reboot
> recovery situation.
> Even in the case where we are in the initial mount, it also doesn't
> distinguish between transient errors such as NFS4ERR_DELAY or reboot
> errors such as NFS4ERR_STALE_CLIENTID, etc.

> Exactly what is the scenario that is causing your hang? Let's try to
> address that with a more targeted fix.

(re-sending with the correct subject, previous mistake was due to my tools failure)

The scenario is as follows: there are several NFS servers and several
production machines with multiple NFS mounts. This is a containerized
multi-tennant workflow so every tennant gets its own NFS mount to access their
data. At some point nfs41_init_clientid fails in the initial mount.nfs call
and all subsequent mount.nfs calls just hang in nfs_wait_client_init_complete
until the original one, where nfs4_proc_exchange_id has failed, is killed.

The cause of the nfs41_init_clientid failure in the production case is a timeout.
The following error message is observed in logs:
  NFS: state manager: lease expired failed on NFSv4 server <ip> with error 110