tracing: Have the reg function allow to fail

Some tracepoints have a registration function that gets enabled when the
tracepoint is enabled. There may be cases that the registraction function
must fail (for example, can't allocate enough memory). In this case, the
tracepoint should also fail to register, otherwise the user would not know
why the tracepoint is not working.

Cc: David Howells <dhowells@redhat.com>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

arch/powerpc/platforms/powernv/opal-tracepoints.c

@@ -6,9 +6,10 @@
 #ifdef HAVE_JUMP_LABEL
 struct static_key opal_tracepoint_key = STATIC_KEY_INIT;
 
-void opal_tracepoint_regfunc(void)
+int opal_tracepoint_regfunc(void)
 {
 	static_key_slow_inc(&opal_tracepoint_key);
+	return 0;
 }
 
 void opal_tracepoint_unregfunc(void)
@@ -25,9 +26,10 @@ void opal_tracepoint_unregfunc(void)
 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
 extern long opal_tracepoint_refcount;
 
-void opal_tracepoint_regfunc(void)
+int opal_tracepoint_regfunc(void)
 {
 	opal_tracepoint_refcount++;
+	return 0;
 }
 
 void opal_tracepoint_unregfunc(void)