NFSv4.1: There is no need to init the session more than once...

Set up a flag to ensure that is indeed the case.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4_fs.h

@@ -49,6 +49,7 @@ enum nfs4_client_state {
 };
 
 enum nfs4_session_state {
+	NFS4_SESSION_INITING,
 	NFS4_SESSION_DRAINING,
 };
 

fs/nfs/nfs4proc.c

@@ -4807,6 +4807,8 @@ struct nfs4_session *nfs4_alloc_session(struct nfs_client *clp)
 	spin_lock_init(&tbl->slot_tbl_lock);
 	rpc_init_wait_queue(&tbl->slot_tbl_waitq, "BackChannel Slot table");
 
+	session->session_state = 1<<NFS4_SESSION_INITING;
+
 	session->clp = clp;
 	return session;
 }
@@ -5023,6 +5025,10 @@ int nfs4_init_session(struct nfs_server *server)
 	if (!nfs4_has_session(clp))
 		return 0;
 
+	session = clp->cl_session;
+	if (!test_and_clear_bit(NFS4_SESSION_INITING, &session->session_state))
+		return 0;
+
 	rsize = server->rsize;
 	if (rsize == 0)
 		rsize = NFS_MAX_FILE_IO_SIZE;
@@ -5030,7 +5036,6 @@ int nfs4_init_session(struct nfs_server *server)
 	if (wsize == 0)
 		wsize = NFS_MAX_FILE_IO_SIZE;
 
-	session = clp->cl_session;
 	session->fc_attrs.max_rqst_sz = wsize + nfs41_maxwrite_overhead;
 	session->fc_attrs.max_resp_sz = rsize + nfs41_maxread_overhead;