linux-kernel - [RFC PATCH 2/8] static_call: Provide DEFINE_STATIC_CALL

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Date:   Mon, 18 Jan 2021 15:12:17 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Michal Hocko <mhocko@...e.com>
Subject: [RFC PATCH 2/8] 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@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Paul E. McKenney <paulmck@...nel.org>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 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 9f05d60aca70..076f124c957a 100644
--- a/include/linux/static_call.h
+++ b/include/linux/static_call.h
@@ -160,13 +160,13 @@ extern void __static_call_update(struct static_call_key *key, void *tramp, void
 extern int static_call_mod_init(struct module *mod);
 extern int static_call_text_reserved(void *start, void *end);
 
-#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);				\
@@ -195,12 +195,12 @@ 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);				\
@@ -242,10 +242,10 @@ 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,					\
 	}
 
 #define DEFINE_STATIC_CALL_NULL(name, _func)				\
@@ -297,4 +297,10 @@ 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 */
-- 
2.25.1