[PATCH] Fix: sparse warnings in tracepoint.c

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

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:392:3: warning: ‘return’ with a value, in function returning void [enabled by default]
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?

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/tracepoint.h      |    5 +++++
 include/trace/events/syscalls.h |    3 ---
 kernel/tracepoint.c             |    8 +++++---
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 08150e2..abab285 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -81,6 +81,11 @@ 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 */
diff --git a/include/trace/events/syscalls.h b/include/trace/events/syscalls.h
index 5a4c04a..14e49c7 100644
--- a/include/trace/events/syscalls.h
+++ b/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),
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 8c4f2f4..f39bb79 100644
--- a/kernel/tracepoint.c
+++ b/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);
@@ -389,7 +391,7 @@ static void tracepoint_module_going(struct module *mod)
 	struct tp_module *tp_mod;
 
 	if (!mod->num_tracepoints)
-		return 0;
+		return;
 
 	mutex_lock(&tracepoint_module_list_mutex);
 	list_for_each_entry(tp_mod, &tracepoint_module_list, list) {
-- 
1.7.10.4