NFSD: Add an nfsd_cb_lm_notify tracepoint

When the server kicks off a CB_LM_NOTIFY callback, record its
arguments so we can better observe asynchronous locking behavior.
For example:

            nfsd-998   [002]  1471.705873: nfsd_cb_notify_lock:  addr=192.168.2.51:0 client 6092a47c:35a43fc1 fh_hash=0x8950b23a
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -6451,8 +6451,10 @@ nfsd4_lm_notify(struct file_lock *fl)
 	}
 	spin_unlock(&nn->blocked_locks_lock);
 
-	if (queue)
+	if (queue) {
+		trace_nfsd_cb_notify_lock(lo, nbl);
 		nfsd4_run_cb(&nbl->nbl_cb);
+	}
 }
 
 static const struct lock_manager_operations nfsd_posix_mng_ops  = {

fs/nfsd/trace.h

@@ -1027,6 +1027,32 @@ TRACE_EVENT(nfsd_cb_done,
 		__entry->status)
 );
 
+TRACE_EVENT(nfsd_cb_notify_lock,
+	TP_PROTO(
+		const struct nfs4_lockowner *lo,
+		const struct nfsd4_blocked_lock *nbl
+	),
+	TP_ARGS(lo, nbl),
+	TP_STRUCT__entry(
+		__field(u32, cl_boot)
+		__field(u32, cl_id)
+		__field(u32, fh_hash)
+		__array(unsigned char, addr, sizeof(struct sockaddr_in6))
+	),
+	TP_fast_assign(
+		const struct nfs4_client *clp = lo->lo_owner.so_client;
+
+		__entry->cl_boot = clp->cl_clientid.cl_boot;
+		__entry->cl_id = clp->cl_clientid.cl_id;
+		__entry->fh_hash = knfsd_fh_hash(&nbl->nbl_fh);
+		memcpy(__entry->addr, &clp->cl_cb_conn.cb_addr,
+			sizeof(struct sockaddr_in6));
+	),
+	TP_printk("addr=%pISpc client %08x:%08x fh_hash=0x%08x",
+		__entry->addr, __entry->cl_boot, __entry->cl_id,
+		__entry->fh_hash)
+);
+
 #endif /* _NFSD_TRACE_H */
 
 #undef TRACE_INCLUDE_PATH