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/pseries/lpar.c

@@ -661,9 +661,10 @@ EXPORT_SYMBOL(arch_free_page);
 #ifdef HAVE_JUMP_LABEL
 struct static_key hcall_tracepoint_key = STATIC_KEY_INIT;
 
-void hcall_tracepoint_regfunc(void)
+int hcall_tracepoint_regfunc(void)
 {
 	static_key_slow_inc(&hcall_tracepoint_key);
+	return 0;
 }
 
 void hcall_tracepoint_unregfunc(void)
@@ -680,9 +681,10 @@ void hcall_tracepoint_unregfunc(void)
 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
 extern long hcall_tracepoint_refcount;
 
-void hcall_tracepoint_regfunc(void)
+int hcall_tracepoint_regfunc(void)
 {
 	hcall_tracepoint_refcount++;
+	return 0;
 }
 
 void hcall_tracepoint_unregfunc(void)