tracepoint: Fix sparse warnings in tracepoint.c

Fix the following sparse warnings:

  CHECK   kernel/tracepoint.c
kernel/tracepoint.c:184:18: warning: incorrect type in assignment (different address spaces)
kernel/tracepoint.c:184:18:    expected struct tracepoint_func *tp_funcs
kernel/tracepoint.c:184:18:    got struct tracepoint_func [noderef] <asn:4>*funcs
kernel/tracepoint.c:216:18: warning: incorrect type in assignment (different address spaces)
kernel/tracepoint.c:216:18:    expected struct tracepoint_func *tp_funcs
kernel/tracepoint.c:216:18:    got struct tracepoint_func [noderef] <asn:4>*funcs
kernel/tracepoint.c:392:24: error: return expression in void function
  CC      kernel/tracepoint.o
kernel/tracepoint.c: In function tracepoint_module_going:
kernel/tracepoint.c:491:6: warning: symbol 'syscall_regfunc' was not declared. Should it be static?
kernel/tracepoint.c:508:6: warning: symbol 'syscall_unregfunc' was not declared. Should it be static?

Link: http://lkml.kernel.org/r/1397049883-28692-1-git-send-email-mathieu.desnoyers@efficios.com

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/linux/tracepoint.h

@@ -80,6 +80,11 @@ static inline void tracepoint_synchronize_unregister(void)
 	synchronize_sched();
 }
 
+#ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
+extern void syscall_regfunc(void);
+extern void syscall_unregfunc(void);
+#endif /* CONFIG_HAVE_SYSCALL_TRACEPOINTS */
+
 #define PARAMS(args...) args
 
 #endif /* _LINUX_TRACEPOINT_H */

include/trace/events/syscalls.h

@@ -13,9 +13,6 @@
 
 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
 
-extern void syscall_regfunc(void);
-extern void syscall_unregfunc(void);
-
 TRACE_EVENT_FN(sys_enter,
 
 	TP_PROTO(struct pt_regs *regs, long id),

kernel/tracepoint.c

@@ -181,7 +181,8 @@ static int tracepoint_add_func(struct tracepoint *tp,
 	if (tp->regfunc && !static_key_enabled(&tp->key))
 		tp->regfunc();
 
-	tp_funcs = tp->funcs;
+	tp_funcs = rcu_dereference_protected(tp->funcs,
+			lockdep_is_held(&tracepoints_mutex));
 	old = func_add(&tp_funcs, func);
 	if (IS_ERR(old)) {
 		WARN_ON_ONCE(1);
@@ -213,7 +214,8 @@ static int tracepoint_remove_func(struct tracepoint *tp,
 {
 	struct tracepoint_func *old, *tp_funcs;
 
-	tp_funcs = tp->funcs;
+	tp_funcs = rcu_dereference_protected(tp->funcs,
+			lockdep_is_held(&tracepoints_mutex));
 	old = func_remove(&tp_funcs, func);
 	if (IS_ERR(old)) {
 		WARN_ON_ONCE(1);