1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef __ASM_PREEMPT_H 3 #define __ASM_PREEMPT_H 4 5 #include <asm/rmwcc.h> 6 #include <asm/percpu.h> 7 8 #include <linux/static_call_types.h> 9 10 DECLARE_PER_CPU_CACHE_HOT(unsigned long, __preempt_count); 11 12 /* 13 * We use the MSB for PREEMPT_NEED_RESCHED mostly because it is available. 14 */ 15 #define PREEMPT_NEED_RESCHED (~(((unsigned long)-1L) >> 1)) 16 17 #ifdef CONFIG_HAS_SEPARATE_PREEMPT_RESCHED_BITS 18 #define __pc_dec "decq" 19 #define __pc_op(op, ...) raw_cpu_##op##_8(__VA_ARGS__) 20 #else 21 #define __pc_dec "decl" 22 #define __pc_op(op, ...) raw_cpu_##op##_4(__VA_ARGS__) 23 #endif 24 25 /* 26 * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such 27 * that a decrement hitting 0 means we can and should reschedule. 28 */ 29 #define PREEMPT_ENABLED (0 + PREEMPT_NEED_RESCHED) 30 31 /* 32 * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users 33 * that think a non-zero value indicates we cannot preempt. 34 */ 35 static __always_inline int preempt_count(void) 36 { 37 return __pc_op(read, __preempt_count) & ~PREEMPT_NEED_RESCHED; 38 } 39 40 /* 41 * unsigned long preempt count parameter works for both 32bit and 64bit cases: 42 * 43 * - For 32bit, "int" (the return of preempt_count()) and "unsigned long" have 44 * the same size. 45 * - For 64bit, the effective bits of a preempt count sit in 32bit, and we 46 * preserve the NEED_RESCHED bit from the old count. 47 */ 48 static __always_inline void preempt_count_set(unsigned long pc) 49 { 50 unsigned long old, new; 51 52 old = __pc_op(read, __preempt_count); 53 do { 54 new = (old & PREEMPT_NEED_RESCHED) | 55 (pc & ~PREEMPT_NEED_RESCHED); 56 } while (!__pc_op(try_cmpxchg, __preempt_count, &old, new)); 57 } 58 59 /* 60 * must be macros to avoid header recursion hell 61 */ 62 #define init_task_preempt_count(p) do { } while (0) 63 64 #define init_idle_preempt_count(p, cpu) do { \ 65 per_cpu(__preempt_count, (cpu)) = PREEMPT_DISABLED; \ 66 } while (0) 67 68 /* 69 * We fold the NEED_RESCHED bit into the preempt count such that 70 * preempt_enable() can decrement and test for needing to reschedule with a 71 * single instruction. 72 * 73 * We invert the actual bit, so that when the decrement hits 0 we know we both 74 * need to resched (the bit is cleared) and can resched (no preempt count). 75 */ 76 77 static __always_inline void set_preempt_need_resched(void) 78 { 79 __pc_op(and, __preempt_count, ~PREEMPT_NEED_RESCHED); 80 } 81 82 static __always_inline void clear_preempt_need_resched(void) 83 { 84 __pc_op(or, __preempt_count, PREEMPT_NEED_RESCHED); 85 } 86 87 static __always_inline bool test_preempt_need_resched(void) 88 { 89 return !(__pc_op(read, __preempt_count) & PREEMPT_NEED_RESCHED); 90 } 91 92 /* 93 * The various preempt_count add/sub methods 94 */ 95 96 static __always_inline void __preempt_count_add(int val) 97 { 98 __pc_op(add, __preempt_count, val); 99 } 100 101 static __always_inline void __preempt_count_sub(int val) 102 { 103 __pc_op(add, __preempt_count, -val); 104 } 105 106 static __always_inline int __preempt_count_add_return(int val) 107 { 108 return __pc_op(add_return, __preempt_count, val); 109 } 110 111 static __always_inline int __preempt_count_sub_return(int val) 112 { 113 return __pc_op(add_return, __preempt_count, -val); 114 } 115 116 /* 117 * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule 118 * a decrement which hits zero means we have no preempt_count and should 119 * reschedule. 120 */ 121 static __always_inline bool __preempt_count_dec_and_test(void) 122 { 123 return GEN_UNARY_RMWcc(__pc_dec, __my_cpu_var(__preempt_count), e, 124 __percpu_arg([var])); 125 } 126 127 /* 128 * Returns true when we need to resched and can (barring IRQ state). 129 */ 130 static __always_inline bool should_resched(int preempt_offset) 131 { 132 return unlikely(__pc_op(read, __preempt_count) == preempt_offset); 133 } 134 135 #ifdef CONFIG_PREEMPTION 136 137 extern asmlinkage void preempt_schedule(void); 138 extern asmlinkage void preempt_schedule_thunk(void); 139 140 #define preempt_schedule_dynamic_enabled preempt_schedule_thunk 141 #define preempt_schedule_dynamic_disabled NULL 142 143 extern asmlinkage void preempt_schedule_notrace(void); 144 extern asmlinkage void preempt_schedule_notrace_thunk(void); 145 146 #define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace_thunk 147 #define preempt_schedule_notrace_dynamic_disabled NULL 148 149 #ifdef CONFIG_PREEMPT_DYNAMIC 150 151 DECLARE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled); 152 153 #define __preempt_schedule() \ 154 do { \ 155 __STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule); \ 156 asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \ 157 } while (0) 158 159 DECLARE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled); 160 161 #define __preempt_schedule_notrace() \ 162 do { \ 163 __STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule_notrace); \ 164 asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule_notrace) : ASM_CALL_CONSTRAINT); \ 165 } while (0) 166 167 #else /* PREEMPT_DYNAMIC */ 168 169 #define __preempt_schedule() \ 170 asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT); 171 172 #define __preempt_schedule_notrace() \ 173 asm volatile ("call preempt_schedule_notrace_thunk" : ASM_CALL_CONSTRAINT); 174 175 #endif /* PREEMPT_DYNAMIC */ 176 177 #endif /* PREEMPTION */ 178 179 #undef __pc_op 180 #undef __pc_dec 181 182 #endif /* __ASM_PREEMPT_H */ 183