NFSv4.1: Handle NFS4ERR_SEQ_MISORDERED when confirming the lease

Apparently the patch "NFS: Always use the same SETCLIENTID boot verifier"
is tickling a Linux nfs server bug, and causing a regression: the server
can get into a situation where it keeps replying NFS4ERR_SEQ_MISORDERED
to our CREATE_SESSION request even when we are sending the correct
sequence ID.

Fix this by purging the lease and then retrying.
Reported-by: NBryan Schumaker <bjschuma@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4state.c

@@ -1580,6 +1580,11 @@ static int nfs4_check_lease(struct nfs_client *clp)
 static int nfs4_handle_reclaim_lease_error(struct nfs_client *clp, int status)
 {
 	switch (status) {
+	case -NFS4ERR_SEQ_MISORDERED:
+		if (test_and_set_bit(NFS4CLNT_PURGE_STATE, &clp->cl_state))
+			return -ESERVERFAULT;
+		/* Lease confirmation error: retry after purging the lease */
+		ssleep(1);
 	case -NFS4ERR_CLID_INUSE:
 	case -NFS4ERR_STALE_CLIENTID:
 		clear_bit(NFS4CLNT_LEASE_CONFIRM, &clp->cl_state);