NFSD: Rename nfsd_cb_state trace point

Make it clear where backchannel state is updated.

Example trace point output:

kworker/u16:0-10    [006]  2800.080404: nfsd_cb_new_state:    addr=192.168.122.6:0 client 65b3c5b8:f541f749 state=UP
         nfsd-940   [003]  2800.478368: nfsd_cb_new_state:    addr=192.168.122.6:0 client 65b3c5b8:f541f749 state=UNKNOWN
kworker/u16:0-10    [003]  2800.478828: nfsd_cb_new_state:    addr=192.168.122.6:0 client 65b3c5b8:f541f749 state=DOWN

kworker/u16:0-10    [005]  2802.039724: nfsd_cb_start:        addr=192.168.122.6:0 client 65b3c5b8:f541f749 state=UP
kworker/u16:0-10    [005]  2810.611452: nfsd_cb_start:        addr=192.168.122.6:0 client 65b3c5b8:f541f749 state=FAULT
kworker/u16:0-10    [005]  2810.616832: nfsd_cb_start:        addr=192.168.122.6:0 client 65b3c5b8:f541f749 state=UNKNOWN
kworker/u16:0-10    [005]  2810.616931: nfsd_cb_start:        addr=192.168.122.6:0 client 65b3c5b8:f541f749 state=DOWN
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4callback.c

@@ -1006,7 +1006,7 @@ static void nfsd4_mark_cb_state(struct nfs4_client *clp, int newstate)
 {
 	if (clp->cl_cb_state != newstate) {
 		clp->cl_cb_state = newstate;
-		trace_nfsd_cb_state(clp);
+		trace_nfsd_cb_new_state(clp);
 	}
 }
 
@@ -1390,6 +1390,8 @@ nfsd4_run_cb_work(struct work_struct *work)
 	struct rpc_clnt *clnt;
 	int flags;
 
+	trace_nfsd_cb_start(clp);
+
 	if (clp->cl_flags & NFSD4_CLIENT_CB_FLAG_MASK)
 		nfsd4_process_cb_update(cb);
 

fs/nfsd/trace.h

@@ -1371,7 +1371,8 @@ DEFINE_EVENT(nfsd_cb_class, nfsd_cb_##name,		\
 	TP_PROTO(const struct nfs4_client *clp),	\
 	TP_ARGS(clp))
 
-DEFINE_NFSD_CB_EVENT(state);
+DEFINE_NFSD_CB_EVENT(start);
+DEFINE_NFSD_CB_EVENT(new_state);
 DEFINE_NFSD_CB_EVENT(probe);
 DEFINE_NFSD_CB_EVENT(lost);
 DEFINE_NFSD_CB_EVENT(shutdown);