[tip: sched/core] static_call: Provide DEFINE_STATIC_CALL_RET0()

[tip-bot2 for Frederic Weisbecker]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     50ace20f2cfecd90c88edaf58400b362f42f2960
Gitweb:        https://git.kernel.org/tip/50ace20f2cfecd90c88edaf58400b362f42f2960
Author:        Frederic Weisbecker <frederic@xxxxxxxxxx>
AuthorDate:    Mon, 18 Jan 2021 15:12:17 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 05 Feb 2021 17:19:55 +01:00

static_call: Provide DEFINE_STATIC_CALL_RET0()

DECLARE_STATIC_CALL() must pass the original function targeted for a
given static call. But DEFINE_STATIC_CALL() may want to initialize it as
off. In this case we can't pass NULL (for functions without return value)
or __static_call_return0 (for functions returning a value) directly
to DEFINE_STATIC_CALL() as that may trigger a static call redeclaration
with a different function prototype. Type casts neither can work around
that as they don't get along with typeof().

The proper way to do that for functions that don't return a value is
to use DEFINE_STATIC_CALL_NULL(). But functions returning a actual value
don't have an equivalent yet.

Provide DEFINE_STATIC_CALL_RET0() to solve this situation.

Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210118141223.123667-3-frederic@xxxxxxxxxx
---
 include/linux/static_call.h | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/include/linux/static_call.h b/include/linux/static_call.h
index bd6735d..d69dd8b 100644
--- a/include/linux/static_call.h
+++ b/include/linux/static_call.h
@@ -144,13 +144,13 @@ extern int static_call_text_reserved(void *start, void *end);
 
 extern long __static_call_return0(void);
 
-#define DEFINE_STATIC_CALL(name, _func)					\
+#define __DEFINE_STATIC_CALL(name, _func, _func_init)			\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\
-		.func = _func,						\
+		.func = _func_init,					\
 		.type = 1,						\
 	};								\
-	ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func)
+	ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func_init)
 
 #define DEFINE_STATIC_CALL_NULL(name, _func)				\
 	DECLARE_STATIC_CALL(name, _func);				\
@@ -178,12 +178,12 @@ struct static_call_key {
 	void *func;
 };
 
-#define DEFINE_STATIC_CALL(name, _func)					\
+#define __DEFINE_STATIC_CALL(name, _func, _func_init)			\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\
-		.func = _func,						\
+		.func = _func_init,					\
 	};								\
-	ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func)
+	ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func_init)
 
 #define DEFINE_STATIC_CALL_NULL(name, _func)				\
 	DECLARE_STATIC_CALL(name, _func);				\
@@ -234,10 +234,10 @@ static inline long __static_call_return0(void)
 	return 0;
 }
 
-#define DEFINE_STATIC_CALL(name, _func)					\
+#define __DEFINE_STATIC_CALL(name, _func, _func_init)			\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\
-		.func = _func,						\
+		.func = _func_init,					\
 	}
 
 #define DEFINE_STATIC_CALL_NULL(name, _func)				\
@@ -286,4 +286,10 @@ static inline int static_call_text_reserved(void *start, void *end)
 
 #endif /* CONFIG_HAVE_STATIC_CALL */
 
+#define DEFINE_STATIC_CALL(name, _func)					\
+	__DEFINE_STATIC_CALL(name, _func, _func)
+
+#define DEFINE_STATIC_CALL_RET0(name, _func)				\
+	__DEFINE_STATIC_CALL(name, _func, __static_call_return0)
+
 #endif /* _LINUX_STATIC_CALL_H */