preempt: Tune preemption flavour on boot v4

index ca9a380..9442c41 100644
@@ -11,14 +11,26 @@ enum insn_type {
 	RET = 3,  /* tramp / site cond-tail-call */
 };
 
+/*
+ * data16 data16 xorq %rax, %rax - a single 5 byte instruction that clears %rax
+ * The REX.W cancels the effect of any data16.
+ */
+static const u8 xor5rax[] = { 0x66, 0x66, 0x48, 0x31, 0xc0 };
+
 static void __ref __static_call_transform(void *insn, enum insn_type type, void *func)
 {
+	const void *emulate = NULL;
 	int size = CALL_INSN_SIZE;
 	const void *code;
 
 	switch (type) {
 	case CALL:
 		code = text_gen_insn(CALL_INSN_OPCODE, insn, func);
+		if (func == &__static_call_return0) {
+			emulate = code;
+			code = &xor5rax;
+		}
+
 		break;
 
 	case NOP:

@@ -41,7 +53,7 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, void 
 	if (unlikely(system_state == SYSTEM_BOOTING))
 		return text_poke_early(insn, code, size);
 
-	text_poke_bp(insn, code, size, NULL);
+	text_poke_bp(insn, code, size, emulate);
 }
 
 static void __static_call_validate(void *insn, bool tail)

@@ -54,7 +66,8 @@ static void __static_call_validate(void *insn, bool tail)
 			return;
 	} else {
 		if (opcode == CALL_INSN_OPCODE ||
-		    !memcmp(insn, ideal_nops[NOP_ATOMIC5], 5))
+		    !memcmp(insn, ideal_nops[NOP_ATOMIC5], 5) ||
+		    !memcmp(insn, xor5rax, 5))
 			return;
 	}
 

index a2c0645..bd6735d 100644
@@ -142,6 +142,8 @@ 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);
 
+extern long __static_call_return0(void);
+
 #define DEFINE_STATIC_CALL(name, _func)					\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\

@@ -206,6 +208,11 @@ static inline int static_call_text_reserved(void *start, void *end)
 	return 0;
 }
 
+static inline long __static_call_return0(void)
+{
+	return 0;
+}
+
 #define EXPORT_STATIC_CALL(name)					\
 	EXPORT_SYMBOL(STATIC_CALL_KEY(name));				\
 	EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))

@@ -222,6 +229,11 @@ struct static_call_key {
 	void *func;
 };
 
+static inline long __static_call_return0(void)
+{
+	return 0;
+}
+
 #define DEFINE_STATIC_CALL(name, _func)					\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\

index 84565c2..0bc11b5 100644
@@ -438,6 +438,11 @@ int __init static_call_init(void)
 }
 early_initcall(static_call_init);
 
+long __static_call_return0(void)
+{
+	return 0;
+}
+
 #ifdef CONFIG_STATIC_CALL_SELFTEST
 
 static int func_a(int x)

index ca9a380..9442c41 100644
@@ -11,14 +11,26 @@ enum insn_type {
 	RET = 3,  /* tramp / site cond-tail-call */
 };
 
+/*
+ * data16 data16 xorq %rax, %rax - a single 5 byte instruction that clears %rax
+ * The REX.W cancels the effect of any data16.
+ */
+static const u8 xor5rax[] = { 0x66, 0x66, 0x48, 0x31, 0xc0 };
+
 static void __ref __static_call_transform(void *insn, enum insn_type type, void *func)
 {
+	const void *emulate = NULL;
 	int size = CALL_INSN_SIZE;
 	const void *code;
 
 	switch (type) {
 	case CALL:
 		code = text_gen_insn(CALL_INSN_OPCODE, insn, func);
+		if (func == &__static_call_return0) {
+			emulate = code;
+			code = &xor5rax;
+		}
+
 		break;
 
 	case NOP:

@@ -41,7 +53,7 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, void 
 	if (unlikely(system_state == SYSTEM_BOOTING))
 		return text_poke_early(insn, code, size);
 
-	text_poke_bp(insn, code, size, NULL);
+	text_poke_bp(insn, code, size, emulate);
 }
 
 static void __static_call_validate(void *insn, bool tail)

@@ -54,7 +66,8 @@ static void __static_call_validate(void *insn, bool tail)
 			return;
 	} else {
 		if (opcode == CALL_INSN_OPCODE ||
-		    !memcmp(insn, ideal_nops[NOP_ATOMIC5], 5))
+		    !memcmp(insn, ideal_nops[NOP_ATOMIC5], 5) ||
+		    !memcmp(insn, xor5rax, 5))
 			return;
 	}
 

index a2c0645..bd6735d 100644
@@ -142,6 +142,8 @@ 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);
 
+extern long __static_call_return0(void);
+
 #define DEFINE_STATIC_CALL(name, _func)					\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\

@@ -206,6 +208,11 @@ static inline int static_call_text_reserved(void *start, void *end)
 	return 0;
 }
 
+static inline long __static_call_return0(void)
+{
+	return 0;
+}
+
 #define EXPORT_STATIC_CALL(name)					\
 	EXPORT_SYMBOL(STATIC_CALL_KEY(name));				\
 	EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))

@@ -222,6 +229,11 @@ struct static_call_key {
 	void *func;
 };
 
+static inline long __static_call_return0(void)
+{
+	return 0;
+}
+
 #define DEFINE_STATIC_CALL(name, _func)					\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\

index 84565c2..0bc11b5 100644
@@ -438,6 +438,11 @@ int __init static_call_init(void)
 }
 early_initcall(static_call_init);
 
+long __static_call_return0(void)
+{
+	return 0;
+}
+
 #ifdef CONFIG_STATIC_CALL_SELFTEST
 
 static int func_a(int x)

index bd6735d..d69dd8b 100644
@@ -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 */

index bd6735d..d69dd8b 100644
@@ -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 */

index 695da4c..a2c0645 100644
@@ -107,26 +107,10 @@ extern void arch_static_call_transform(void *site, void *tramp, void *func, bool
 
 #define STATIC_CALL_TRAMP_ADDR(name) &STATIC_CALL_TRAMP(name)
 
-/*
- * __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from
- * the symbol table so that objtool can reference it when it generates the
- * .static_call_sites section.
- */
-#define __static_call(name)						\
-({									\
-	__ADDRESSABLE(STATIC_CALL_KEY(name));				\
-	&STATIC_CALL_TRAMP(name);					\
-})
-
 #else
 #define STATIC_CALL_TRAMP_ADDR(name) NULL
 #endif
 
-
-#define DECLARE_STATIC_CALL(name, func)					\
-	extern struct static_call_key STATIC_CALL_KEY(name);		\
-	extern typeof(func) STATIC_CALL_TRAMP(name);
-
 #define static_call_update(name, func)					\
 ({									\
 	BUILD_BUG_ON(!__same_type(*(func), STATIC_CALL_TRAMP(name)));	\

@@ -174,7 +158,6 @@ extern int static_call_text_reserved(void *start, void *end);
 	};								\
 	ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)
 
-#define static_call(name)	__static_call(name)
 #define static_call_cond(name)	(void)__static_call(name)
 
 #define EXPORT_STATIC_CALL(name)					\

@@ -207,7 +190,6 @@ struct static_call_key {
 	};								\
 	ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)
 
-#define static_call(name)	__static_call(name)
 #define static_call_cond(name)	(void)__static_call(name)
 
 static inline

@@ -252,9 +234,6 @@ struct static_call_key {
 		.func = NULL,						\
 	}
 
-#define static_call(name)						\
-	((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func))
-
 static inline void __static_call_nop(void) { }
 
 /*

index 89135bb..08f78b1 100644
@@ -4,6 +4,7 @@
 
 #include <linux/types.h>
 #include <linux/stringify.h>
+#include <linux/compiler.h>
 
 #define STATIC_CALL_KEY_PREFIX		__SCK__
 #define STATIC_CALL_KEY_PREFIX_STR	__stringify(STATIC_CALL_KEY_PREFIX)

@@ -32,4 +33,30 @@ struct static_call_site {
 	s32 key;
 };
 
+#define DECLARE_STATIC_CALL(name, func)					\
+	extern struct static_call_key STATIC_CALL_KEY(name);		\
+	extern typeof(func) STATIC_CALL_TRAMP(name);
+
+#ifdef CONFIG_HAVE_STATIC_CALL
+
+/*
+ * __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from
+ * the symbol table so that objtool can reference it when it generates the
+ * .static_call_sites section.
+ */
+#define __static_call(name)						\
+({									\
+	__ADDRESSABLE(STATIC_CALL_KEY(name));				\
+	&STATIC_CALL_TRAMP(name);					\
+})
+
+#define static_call(name)	__static_call(name)
+
+#else
+
+#define static_call(name)						\
+	((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func))
+
+#endif /* CONFIG_HAVE_STATIC_CALL */
+
 #endif /* _STATIC_CALL_TYPES_H */

index 89135bb..08f78b1 100644
@@ -4,6 +4,7 @@
 
 #include <linux/types.h>
 #include <linux/stringify.h>
+#include <linux/compiler.h>
 
 #define STATIC_CALL_KEY_PREFIX		__SCK__
 #define STATIC_CALL_KEY_PREFIX_STR	__stringify(STATIC_CALL_KEY_PREFIX)

@@ -32,4 +33,30 @@ struct static_call_site {
 	s32 key;
 };
 
+#define DECLARE_STATIC_CALL(name, func)					\
+	extern struct static_call_key STATIC_CALL_KEY(name);		\
+	extern typeof(func) STATIC_CALL_TRAMP(name);
+
+#ifdef CONFIG_HAVE_STATIC_CALL
+
+/*
+ * __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from
+ * the symbol table so that objtool can reference it when it generates the
+ * .static_call_sites section.
+ */
+#define __static_call(name)						\
+({									\
+	__ADDRESSABLE(STATIC_CALL_KEY(name));				\
+	&STATIC_CALL_TRAMP(name);					\
+})
+
+#define static_call(name)	__static_call(name)
+
+#else
+
+#define static_call(name)						\
+	((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func))
+
+#endif /* CONFIG_HAVE_STATIC_CALL */
+
 #endif /* _STATIC_CALL_TYPES_H */

index 695da4c..a2c0645 100644
@@ -107,26 +107,10 @@ extern void arch_static_call_transform(void *site, void *tramp, void *func, bool
 
 #define STATIC_CALL_TRAMP_ADDR(name) &STATIC_CALL_TRAMP(name)
 
-/*
- * __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from
- * the symbol table so that objtool can reference it when it generates the
- * .static_call_sites section.
- */
-#define __static_call(name)						\
-({									\
-	__ADDRESSABLE(STATIC_CALL_KEY(name));				\
-	&STATIC_CALL_TRAMP(name);					\
-})
-
 #else
 #define STATIC_CALL_TRAMP_ADDR(name) NULL
 #endif
 
-
-#define DECLARE_STATIC_CALL(name, func)					\
-	extern struct static_call_key STATIC_CALL_KEY(name);		\
-	extern typeof(func) STATIC_CALL_TRAMP(name);
-
 #define static_call_update(name, func)					\
 ({									\
 	BUILD_BUG_ON(!__same_type(*(func), STATIC_CALL_TRAMP(name)));	\

@@ -174,7 +158,6 @@ extern int static_call_text_reserved(void *start, void *end);
 	};								\
 	ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)
 
-#define static_call(name)	__static_call(name)
 #define static_call_cond(name)	(void)__static_call(name)
 
 #define EXPORT_STATIC_CALL(name)					\

@@ -207,7 +190,6 @@ struct static_call_key {
 	};								\
 	ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)
 
-#define static_call(name)	__static_call(name)
 #define static_call_cond(name)	(void)__static_call(name)
 
 static inline

@@ -252,9 +234,6 @@ struct static_call_key {
 		.func = NULL,						\
 	}
 
-#define static_call(name)						\
-	((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func))
-
 static inline void __static_call_nop(void) { }
 
 /*

index 89135bb..08f78b1 100644
@@ -4,6 +4,7 @@
 
 #include <linux/types.h>
 #include <linux/stringify.h>
+#include <linux/compiler.h>
 
 #define STATIC_CALL_KEY_PREFIX		__SCK__
 #define STATIC_CALL_KEY_PREFIX_STR	__stringify(STATIC_CALL_KEY_PREFIX)

@@ -32,4 +33,30 @@ struct static_call_site {
 	s32 key;
 };
 
+#define DECLARE_STATIC_CALL(name, func)					\
+	extern struct static_call_key STATIC_CALL_KEY(name);		\
+	extern typeof(func) STATIC_CALL_TRAMP(name);
+
+#ifdef CONFIG_HAVE_STATIC_CALL
+
+/*
+ * __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from
+ * the symbol table so that objtool can reference it when it generates the
+ * .static_call_sites section.
+ */
+#define __static_call(name)						\
+({									\
+	__ADDRESSABLE(STATIC_CALL_KEY(name));				\
+	&STATIC_CALL_TRAMP(name);					\
+})
+
+#define static_call(name)	__static_call(name)
+
+#else
+
+#define static_call(name)						\
+	((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func))
+
+#endif /* CONFIG_HAVE_STATIC_CALL */
+
 #endif /* _STATIC_CALL_TYPES_H */

index 89135bb..08f78b1 100644
@@ -4,6 +4,7 @@
 
 #include <linux/types.h>
 #include <linux/stringify.h>
+#include <linux/compiler.h>
 
 #define STATIC_CALL_KEY_PREFIX		__SCK__
 #define STATIC_CALL_KEY_PREFIX_STR	__stringify(STATIC_CALL_KEY_PREFIX)

@@ -32,4 +33,30 @@ struct static_call_site {
 	s32 key;
 };
 
+#define DECLARE_STATIC_CALL(name, func)					\
+	extern struct static_call_key STATIC_CALL_KEY(name);		\
+	extern typeof(func) STATIC_CALL_TRAMP(name);
+
+#ifdef CONFIG_HAVE_STATIC_CALL
+
+/*
+ * __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from
+ * the symbol table so that objtool can reference it when it generates the
+ * .static_call_sites section.
+ */
+#define __static_call(name)						\
+({									\
+	__ADDRESSABLE(STATIC_CALL_KEY(name));				\
+	&STATIC_CALL_TRAMP(name);					\
+})
+
+#define static_call(name)	__static_call(name)
+
+#else
+
+#define static_call(name)						\
+	((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func))
+
+#endif /* CONFIG_HAVE_STATIC_CALL */
+
 #endif /* _STATIC_CALL_TYPES_H */

index f7902d8..cfd3d34 100644
@@ -15,7 +15,7 @@
 #include <linux/typecheck.h>
 #include <linux/printk.h>
 #include <linux/build_bug.h>
-
+#include <linux/static_call_types.h>
 #include <asm/byteorder.h>
 
 #include <uapi/linux/kernel.h>

@@ -81,11 +81,26 @@ struct pt_regs;
 struct user;
 
 #ifdef CONFIG_PREEMPT_VOLUNTARY
-extern int _cond_resched(void);
-# define might_resched() _cond_resched()
+
+extern int __cond_resched(void);
+# define might_resched() __cond_resched()
+
+#elif defined(CONFIG_PREEMPT_DYNAMIC)
+
+extern int __cond_resched(void);
+
+DECLARE_STATIC_CALL(might_resched, __cond_resched);
+
+static __always_inline void might_resched(void)
+{
+	static_call(might_resched)();
+}
+
 #else
+
 # define might_resched() do { } while (0)
-#endif
+
+#endif /* CONFIG_PREEMPT_* */
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 extern void ___might_sleep(const char *file, int line, int preempt_offset);

index e115222..2f35594 100644
@@ -1871,11 +1871,32 @@ static inline int test_tsk_need_resched(struct task_struct *tsk)
  * value indicates whether a reschedule was done in fact.
  * cond_resched_lock() will drop the spinlock before scheduling,
  */
-#ifndef CONFIG_PREEMPTION
-extern int _cond_resched(void);
+#if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC)
+extern int __cond_resched(void);
+
+#ifdef CONFIG_PREEMPT_DYNAMIC
+
+DECLARE_STATIC_CALL(cond_resched, __cond_resched);
+
+static __always_inline int _cond_resched(void)
+{
+	return static_call(cond_resched)();
+}
+
 #else
+
+static inline int _cond_resched(void)
+{
+	return __cond_resched();
+}
+
+#endif /* CONFIG_PREEMPT_DYNAMIC */
+
+#else
+
 static inline int _cond_resched(void) { return 0; }
-#endif
+
+#endif /* !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) */
 
 #define cond_resched() ({			\
 	___might_sleep(__FILE__, __LINE__, 0);	\

index be3a956..bc7b00b 100644
@@ -6771,17 +6771,27 @@ SYSCALL_DEFINE0(sched_yield)
 	return 0;
 }
 
-#ifndef CONFIG_PREEMPTION
-int __sched _cond_resched(void)
+#if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC)
+int __sched __cond_resched(void)
 {
 	if (should_resched(0)) {
 		preempt_schedule_common();
 		return 1;
 	}
+#ifndef CONFIG_PREEMPT_RCU
 	rcu_all_qs();
+#endif
 	return 0;
 }
-EXPORT_SYMBOL(_cond_resched);
+EXPORT_SYMBOL(__cond_resched);
+#endif
+
+#ifdef CONFIG_PREEMPT_DYNAMIC
+DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched);
+EXPORT_STATIC_CALL(cond_resched);
+
+DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched);
+EXPORT_STATIC_CALL(might_resched);
 #endif
 
 /*

index f7902d8..cfd3d34 100644
@@ -15,7 +15,7 @@
 #include <linux/typecheck.h>
 #include <linux/printk.h>
 #include <linux/build_bug.h>
-
+#include <linux/static_call_types.h>
 #include <asm/byteorder.h>
 
 #include <uapi/linux/kernel.h>

@@ -81,11 +81,26 @@ struct pt_regs;
 struct user;
 
 #ifdef CONFIG_PREEMPT_VOLUNTARY
-extern int _cond_resched(void);
-# define might_resched() _cond_resched()
+
+extern int __cond_resched(void);
+# define might_resched() __cond_resched()
+
+#elif defined(CONFIG_PREEMPT_DYNAMIC)
+
+extern int __cond_resched(void);
+
+DECLARE_STATIC_CALL(might_resched, __cond_resched);
+
+static __always_inline void might_resched(void)
+{
+	static_call(might_resched)();
+}
+
 #else
+
 # define might_resched() do { } while (0)
-#endif
+
+#endif /* CONFIG_PREEMPT_* */
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 extern void ___might_sleep(const char *file, int line, int preempt_offset);

index e115222..2f35594 100644
@@ -1871,11 +1871,32 @@ static inline int test_tsk_need_resched(struct task_struct *tsk)
  * value indicates whether a reschedule was done in fact.
  * cond_resched_lock() will drop the spinlock before scheduling,
  */
-#ifndef CONFIG_PREEMPTION
-extern int _cond_resched(void);
+#if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC)
+extern int __cond_resched(void);
+
+#ifdef CONFIG_PREEMPT_DYNAMIC
+
+DECLARE_STATIC_CALL(cond_resched, __cond_resched);
+
+static __always_inline int _cond_resched(void)
+{
+	return static_call(cond_resched)();
+}
+
 #else
+
+static inline int _cond_resched(void)
+{
+	return __cond_resched();
+}
+
+#endif /* CONFIG_PREEMPT_DYNAMIC */
+
+#else
+
 static inline int _cond_resched(void) { return 0; }
-#endif
+
+#endif /* !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) */
 
 #define cond_resched() ({			\
 	___might_sleep(__FILE__, __LINE__, 0);	\

index 4afbdd2..f7c8fd8 100644
@@ -6785,17 +6785,27 @@ SYSCALL_DEFINE0(sched_yield)
 	return 0;
 }
 
-#ifndef CONFIG_PREEMPTION
-int __sched _cond_resched(void)
+#if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC)
+int __sched __cond_resched(void)
 {
 	if (should_resched(0)) {
 		preempt_schedule_common();
 		return 1;
 	}
+#ifndef CONFIG_PREEMPT_RCU
 	rcu_all_qs();
+#endif
 	return 0;
 }
-EXPORT_SYMBOL(_cond_resched);
+EXPORT_SYMBOL(__cond_resched);
+#endif
+
+#ifdef CONFIG_PREEMPT_DYNAMIC
+DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched);
+EXPORT_STATIC_CALL(cond_resched);
+
+DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched);
+EXPORT_STATIC_CALL(might_resched);
 #endif
 
 /*

index 0562992..c659266 100644
@@ -5348,37 +5348,154 @@ EXPORT_STATIC_CALL(preempt_schedule_notrace);
  *   preempt_schedule_notrace   <- preempt_schedule_notrace
  *   irqentry_exit_cond_resched <- irqentry_exit_cond_resched
  */
-static int __init setup_preempt_mode(char *str)
+
+enum {
+	preempt_dynamic_none = 0,
+	preempt_dynamic_voluntary,
+	preempt_dynamic_full,
+};
+
+static int preempt_dynamic_mode = preempt_dynamic_full;
+
+static int sched_dynamic_mode(const char *str)
 {
-	if (!strcmp(str, "none")) {
+	if (!strcmp(str, "none"))
+		return 0;
+
+	if (!strcmp(str, "voluntary"))
+		return 1;
+
+	if (!strcmp(str, "full"))
+		return 2;
+
+	return -1;
+}
+
+static void sched_dynamic_update(int mode)
+{
+	/*
+	 * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
+	 * the ZERO state, which is invalid.
+	 */
+	static_call_update(cond_resched, __cond_resched);
+	static_call_update(might_resched, __cond_resched);
+	static_call_update(preempt_schedule, __preempt_schedule_func);
+	static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
+	static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+
+	switch (mode) {
+	case preempt_dynamic_none:
 		static_call_update(cond_resched, __cond_resched);
 		static_call_update(might_resched, (typeof(&__cond_resched)) __static_call_return0);
 		static_call_update(preempt_schedule, (typeof(&preempt_schedule)) NULL);
 		static_call_update(preempt_schedule_notrace, (typeof(&preempt_schedule_notrace)) NULL);
 		static_call_update(irqentry_exit_cond_resched, (typeof(&irqentry_exit_cond_resched)) NULL);
-		pr_info("Dynamic Preempt: %s\n", str);
-	} else if (!strcmp(str, "voluntary")) {
+		pr_info("Dynamic Preempt: none\n");
+		break;
+
+	case preempt_dynamic_voluntary:
 		static_call_update(cond_resched, __cond_resched);
 		static_call_update(might_resched, __cond_resched);
 		static_call_update(preempt_schedule, (typeof(&preempt_schedule)) NULL);
 		static_call_update(preempt_schedule_notrace, (typeof(&preempt_schedule_notrace)) NULL);
 		static_call_update(irqentry_exit_cond_resched, (typeof(&irqentry_exit_cond_resched)) NULL);
-		pr_info("Dynamic Preempt: %s\n", str);
-	} else if (!strcmp(str, "full")) {
+		pr_info("Dynamic Preempt: voluntary\n");
+		break;
+
+	case preempt_dynamic_full:
 		static_call_update(cond_resched, (typeof(&__cond_resched)) __static_call_return0);
 		static_call_update(might_resched, (typeof(&__cond_resched)) __static_call_return0);
 		static_call_update(preempt_schedule, __preempt_schedule_func);
 		static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
 		static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
-		pr_info("Dynamic Preempt: %s\n", str);
-	} else {
-		pr_warn("Dynamic Preempt: Unsupported preempt mode %s, default to full\n", str);
+		pr_info("Dynamic Preempt: full\n");
+		break;
+	}
+
+	preempt_dynamic_mode = mode;
+}
+
+static int __init setup_preempt_mode(char *str)
+{
+	int mode = sched_dynamic_mode(str);
+	if (mode < 0) {
+		pr_warn("Dynamic Preempt: unsupported mode: %s\n", str);
 		return 1;
 	}
+
+	sched_dynamic_update(mode);
 	return 0;
 }
 __setup("preempt=", setup_preempt_mode);
 
+#ifdef CONFIG_SCHED_DEBUG
+
+static ssize_t sched_dynamic_write(struct file *filp, const char __user *ubuf,
+				   size_t cnt, loff_t *ppos)
+{
+	char buf[16];
+	int mode;
+
+	if (cnt > 15)
+		cnt = 15;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+	mode = sched_dynamic_mode(strstrip(buf));
+	if (mode < 0)
+		return mode;
+
+	sched_dynamic_update(mode);
+
+	*ppos += cnt;
+
+	return cnt;
+}
+
+static int sched_dynamic_show(struct seq_file *m, void *v)
+{
+	static const char * preempt_modes[] = {
+		"none", "voluntary", "full"
+	};
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(preempt_modes); i++) {
+		if (preempt_dynamic_mode == i)
+			seq_puts(m, "(");
+		seq_puts(m, preempt_modes[i]);
+		if (preempt_dynamic_mode == i)
+			seq_puts(m, ")");
+
+		seq_puts(m, " ");
+	}
+
+	seq_puts(m, "\n");
+	return 0;
+}
+
+static int sched_dynamic_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, sched_dynamic_show, NULL);
+}
+
+static const struct file_operations sched_dynamic_fops = {
+	.open		= sched_dynamic_open,
+	.write		= sched_dynamic_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static __init int sched_init_debug_dynamic(void)
+{
+	debugfs_create_file("sched_preempt", 0644, NULL, NULL, &sched_dynamic_fops);
+	return 0;
+}
+late_initcall(sched_init_debug_dynamic);
+
+#endif /* CONFIG_SCHED_DEBUG */
 #endif /* CONFIG_PREEMPT_DYNAMIC */
 
 

index 220393d..cb226f7 100644
@@ -5349,37 +5349,154 @@ EXPORT_STATIC_CALL(preempt_schedule_notrace);
  *   preempt_schedule_notrace   <- preempt_schedule_notrace
  *   irqentry_exit_cond_resched <- irqentry_exit_cond_resched
  */
-static int __init setup_preempt_mode(char *str)
+
+enum {
+	preempt_dynamic_none = 0,
+	preempt_dynamic_voluntary,
+	preempt_dynamic_full,
+};
+
+static int preempt_dynamic_mode = preempt_dynamic_full;
+
+static int sched_dynamic_mode(const char *str)
 {
-	if (!strcmp(str, "none")) {
+	if (!strcmp(str, "none"))
+		return 0;
+
+	if (!strcmp(str, "voluntary"))
+		return 1;
+
+	if (!strcmp(str, "full"))
+		return 2;
+
+	return -1;
+}
+
+static void sched_dynamic_update(int mode)
+{
+	/*
+	 * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
+	 * the ZERO state, which is invalid.
+	 */
+	static_call_update(cond_resched, __cond_resched);
+	static_call_update(might_resched, __cond_resched);
+	static_call_update(preempt_schedule, __preempt_schedule_func);
+	static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
+	static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+
+	switch (mode) {
+	case preempt_dynamic_none:
 		static_call_update(cond_resched, __cond_resched);
 		static_call_update(might_resched, (typeof(&__cond_resched)) __static_call_return0);
 		static_call_update(preempt_schedule, (typeof(&preempt_schedule)) NULL);
 		static_call_update(preempt_schedule_notrace, (typeof(&preempt_schedule_notrace)) NULL);
 		static_call_update(irqentry_exit_cond_resched, (typeof(&irqentry_exit_cond_resched)) NULL);
-		pr_info("Dynamic Preempt: %s\n", str);
-	} else if (!strcmp(str, "voluntary")) {
+		pr_info("Dynamic Preempt: none\n");
+		break;
+
+	case preempt_dynamic_voluntary:
 		static_call_update(cond_resched, __cond_resched);
 		static_call_update(might_resched, __cond_resched);
 		static_call_update(preempt_schedule, (typeof(&preempt_schedule)) NULL);
 		static_call_update(preempt_schedule_notrace, (typeof(&preempt_schedule_notrace)) NULL);
 		static_call_update(irqentry_exit_cond_resched, (typeof(&irqentry_exit_cond_resched)) NULL);
-		pr_info("Dynamic Preempt: %s\n", str);
-	} else if (!strcmp(str, "full")) {
+		pr_info("Dynamic Preempt: voluntary\n");
+		break;
+
+	case preempt_dynamic_full:
 		static_call_update(cond_resched, (typeof(&__cond_resched)) __static_call_return0);
 		static_call_update(might_resched, (typeof(&__cond_resched)) __static_call_return0);
 		static_call_update(preempt_schedule, __preempt_schedule_func);
 		static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
 		static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
-		pr_info("Dynamic Preempt: %s\n", str);
-	} else {
-		pr_warn("Dynamic Preempt: Unsupported preempt mode %s, default to full\n", str);
+		pr_info("Dynamic Preempt: full\n");
+		break;
+	}
+
+	preempt_dynamic_mode = mode;
+}
+
+static int __init setup_preempt_mode(char *str)
+{
+	int mode = sched_dynamic_mode(str);
+	if (mode < 0) {
+		pr_warn("Dynamic Preempt: unsupported mode: %s\n", str);
 		return 1;
 	}
+
+	sched_dynamic_update(mode);
 	return 0;
 }
 __setup("preempt=", setup_preempt_mode);
 
+#ifdef CONFIG_SCHED_DEBUG
+
+static ssize_t sched_dynamic_write(struct file *filp, const char __user *ubuf,
+				   size_t cnt, loff_t *ppos)
+{
+	char buf[16];
+	int mode;
+
+	if (cnt > 15)
+		cnt = 15;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+	mode = sched_dynamic_mode(strstrip(buf));
+	if (mode < 0)
+		return mode;
+
+	sched_dynamic_update(mode);
+
+	*ppos += cnt;
+
+	return cnt;
+}
+
+static int sched_dynamic_show(struct seq_file *m, void *v)
+{
+	static const char * preempt_modes[] = {
+		"none", "voluntary", "full"
+	};
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(preempt_modes); i++) {
+		if (preempt_dynamic_mode == i)
+			seq_puts(m, "(");
+		seq_puts(m, preempt_modes[i]);
+		if (preempt_dynamic_mode == i)
+			seq_puts(m, ")");
+
+		seq_puts(m, " ");
+	}
+
+	seq_puts(m, "\n");
+	return 0;
+}
+
+static int sched_dynamic_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, sched_dynamic_show, NULL);
+}
+
+static const struct file_operations sched_dynamic_fops = {
+	.open		= sched_dynamic_open,
+	.write		= sched_dynamic_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static __init int sched_init_debug_dynamic(void)
+{
+	debugfs_create_file("sched_preempt", 0644, NULL, NULL, &sched_dynamic_fops);
+	return 0;
+}
+late_initcall(sched_init_debug_dynamic);
+
+#endif /* CONFIG_SCHED_DEBUG */
 #endif /* CONFIG_PREEMPT_DYNAMIC */
 
 

index 0c06717..4a17bb5 100644
@@ -5363,37 +5363,154 @@ EXPORT_STATIC_CALL(preempt_schedule_notrace);
  *   preempt_schedule_notrace   <- preempt_schedule_notrace
  *   irqentry_exit_cond_resched <- irqentry_exit_cond_resched
  */
-static int __init setup_preempt_mode(char *str)
+
+enum {
+	preempt_dynamic_none = 0,
+	preempt_dynamic_voluntary,
+	preempt_dynamic_full,
+};
+
+static int preempt_dynamic_mode = preempt_dynamic_full;
+
+static int sched_dynamic_mode(const char *str)
 {
-	if (!strcmp(str, "none")) {
+	if (!strcmp(str, "none"))
+		return 0;
+
+	if (!strcmp(str, "voluntary"))
+		return 1;
+
+	if (!strcmp(str, "full"))
+		return 2;
+
+	return -1;
+}
+
+static void sched_dynamic_update(int mode)
+{
+	/*
+	 * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
+	 * the ZERO state, which is invalid.
+	 */
+	static_call_update(cond_resched, __cond_resched);
+	static_call_update(might_resched, __cond_resched);
+	static_call_update(preempt_schedule, __preempt_schedule_func);
+	static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
+	static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+
+	switch (mode) {
+	case preempt_dynamic_none:
 		static_call_update(cond_resched, __cond_resched);
 		static_call_update(might_resched, (typeof(&__cond_resched)) __static_call_return0);
 		static_call_update(preempt_schedule, (typeof(&preempt_schedule)) NULL);
 		static_call_update(preempt_schedule_notrace, (typeof(&preempt_schedule_notrace)) NULL);
 		static_call_update(irqentry_exit_cond_resched, (typeof(&irqentry_exit_cond_resched)) NULL);
-		pr_info("Dynamic Preempt: %s\n", str);
-	} else if (!strcmp(str, "voluntary")) {
+		pr_info("Dynamic Preempt: none\n");
+		break;
+
+	case preempt_dynamic_voluntary:
 		static_call_update(cond_resched, __cond_resched);
 		static_call_update(might_resched, __cond_resched);
 		static_call_update(preempt_schedule, (typeof(&preempt_schedule)) NULL);
 		static_call_update(preempt_schedule_notrace, (typeof(&preempt_schedule_notrace)) NULL);
 		static_call_update(irqentry_exit_cond_resched, (typeof(&irqentry_exit_cond_resched)) NULL);
-		pr_info("Dynamic Preempt: %s\n", str);
-	} else if (!strcmp(str, "full")) {
+		pr_info("Dynamic Preempt: voluntary\n");
+		break;
+
+	case preempt_dynamic_full:
 		static_call_update(cond_resched, (typeof(&__cond_resched)) __static_call_return0);
 		static_call_update(might_resched, (typeof(&__cond_resched)) __static_call_return0);
 		static_call_update(preempt_schedule, __preempt_schedule_func);
 		static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
 		static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
-		pr_info("Dynamic Preempt: %s\n", str);
-	} else {
-		pr_warn("Dynamic Preempt: Unsupported preempt mode %s, default to full\n", str);
+		pr_info("Dynamic Preempt: full\n");
+		break;
+	}
+
+	preempt_dynamic_mode = mode;
+}
+
+static int __init setup_preempt_mode(char *str)
+{
+	int mode = sched_dynamic_mode(str);
+	if (mode < 0) {
+		pr_warn("Dynamic Preempt: unsupported mode: %s\n", str);
 		return 1;
 	}
+
+	sched_dynamic_update(mode);
 	return 0;
 }
 __setup("preempt=", setup_preempt_mode);
 
+#ifdef CONFIG_SCHED_DEBUG
+
+static ssize_t sched_dynamic_write(struct file *filp, const char __user *ubuf,
+				   size_t cnt, loff_t *ppos)
+{
+	char buf[16];
+	int mode;
+
+	if (cnt > 15)
+		cnt = 15;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+	mode = sched_dynamic_mode(strstrip(buf));
+	if (mode < 0)
+		return mode;
+
+	sched_dynamic_update(mode);
+
+	*ppos += cnt;
+
+	return cnt;
+}
+
+static int sched_dynamic_show(struct seq_file *m, void *v)
+{
+	static const char * preempt_modes[] = {
+		"none", "voluntary", "full"
+	};
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(preempt_modes); i++) {
+		if (preempt_dynamic_mode == i)
+			seq_puts(m, "(");
+		seq_puts(m, preempt_modes[i]);
+		if (preempt_dynamic_mode == i)
+			seq_puts(m, ")");
+
+		seq_puts(m, " ");
+	}
+
+	seq_puts(m, "\n");
+	return 0;
+}
+
+static int sched_dynamic_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, sched_dynamic_show, NULL);
+}
+
+static const struct file_operations sched_dynamic_fops = {
+	.open		= sched_dynamic_open,
+	.write		= sched_dynamic_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static __init int sched_init_debug_dynamic(void)
+{
+	debugfs_create_file("sched_preempt", 0644, NULL, NULL, &sched_dynamic_fops);
+	return 0;
+}
+late_initcall(sched_init_debug_dynamic);
+
+#endif /* CONFIG_SCHED_DEBUG */
 #endif /* CONFIG_PREEMPT_DYNAMIC */