[RFC PATCH 6/8] preempt/dynamic: Provide preempt_schedule[_notrace]() static calls

[Frederic Weisbecker]

From: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>

Provide static calls to control preempt_schedule[_notrace]()
(called in CONFIG_PREEMPT) so that we can override their behaviour when
preempt= is overriden.

Since the default behaviour is full preemption, both their calls are
initialized to the arch provided wrapper, if any.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
[only define static calls when PREEMPT_DYNAMIC, make it less dependent
on x86 with __preempt_schedule_func()]
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
 arch/x86/include/asm/preempt.h | 34 ++++++++++++++++++++++++++--------
 kernel/sched/core.c            | 12 ++++++++++++
 2 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index 69485ca13665..3db9cb8b1a25 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -5,6 +5,7 @@
 #include <asm/rmwcc.h>
 #include <asm/percpu.h>
 #include <linux/thread_info.h>
+#include <linux/static_call_types.h>
 
 DECLARE_PER_CPU(int, __preempt_count);
 
@@ -103,16 +104,33 @@ static __always_inline bool should_resched(int preempt_offset)
 }
 
 #ifdef CONFIG_PREEMPTION
-  extern asmlinkage void preempt_schedule_thunk(void);
-# define __preempt_schedule() \
-	asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT)
 
-  extern asmlinkage void preempt_schedule(void);
-  extern asmlinkage void preempt_schedule_notrace_thunk(void);
-# define __preempt_schedule_notrace() \
-	asm volatile ("call preempt_schedule_notrace_thunk" : ASM_CALL_CONSTRAINT)
+extern asmlinkage void preempt_schedule(void);
+extern asmlinkage void preempt_schedule_thunk(void);
+
+#define __preempt_schedule_func() preempt_schedule_thunk
+
+DECLARE_STATIC_CALL(preempt_schedule, __preempt_schedule_func());
+
+#define __preempt_schedule() \
+do { \
+	__ADDRESSABLE(STATIC_CALL_KEY(preempt_schedule)); \
+	asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \
+} while (0)
+
+extern asmlinkage void preempt_schedule_notrace(void);
+extern asmlinkage void preempt_schedule_notrace_thunk(void);
+
+#define __preempt_schedule_notrace_func() preempt_schedule_notrace_thunk
+
+DECLARE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func());
+
+#define __preempt_schedule_notrace() \
+do { \
+	__ADDRESSABLE(STATIC_CALL_KEY(preempt_schedule_notrace)); \
+	asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule_notrace) : ASM_CALL_CONSTRAINT); \
+} while (0)
 
-  extern asmlinkage void preempt_schedule_notrace(void);
 #endif
 
 #endif /* __ASM_PREEMPT_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d6de12b4eef2..faff4b546c5f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5251,6 +5251,12 @@ asmlinkage __visible void __sched notrace preempt_schedule(void)
 NOKPROBE_SYMBOL(preempt_schedule);
 EXPORT_SYMBOL(preempt_schedule);
 
+#ifdef CONFIG_PREEMPT_DYNAMIC
+DEFINE_STATIC_CALL(preempt_schedule, __preempt_schedule_func());
+EXPORT_STATIC_CALL(preempt_schedule);
+#endif
+
+
 /**
  * preempt_schedule_notrace - preempt_schedule called by tracing
  *
@@ -5303,6 +5309,12 @@ asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
 }
 EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
 
+#ifdef CONFIG_PREEMPT_DYNAMIC
+DEFINE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func());
+EXPORT_STATIC_CALL(preempt_schedule_notrace);
+#endif
+
+
 #endif /* CONFIG_PREEMPTION */
 
 /*
-- 
2.25.1