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 #include <linux/thread_info.h> 8 9 DECLARE_PER_CPU(int, __preempt_count); 10 11 /* We use the MSB mostly because its available */ 12 #define PREEMPT_NEED_RESCHED 0x80000000 13 14 /* 15 * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such 16 * that a decrement hitting 0 means we can and should reschedule. 17 */ 18 #define PREEMPT_ENABLED (0 + PREEMPT_NEED_RESCHED) 19 20 /* 21 * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users 22 * that think a non-zero value indicates we cannot preempt. 23 */ 24 static __always_inline int preempt_count(void) 25 { 26 return raw_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED; 27 } 28 29 static __always_inline void preempt_count_set(int pc) 30 { 31 int old, new; 32 33 do { 34 old = raw_cpu_read_4(__preempt_count); 35 new = (old & PREEMPT_NEED_RESCHED) | 36 (pc & ~PREEMPT_NEED_RESCHED); 37 } while (raw_cpu_cmpxchg_4(__preempt_count, old, new) != old); 38 } 39 40 /* 41 * must be macros to avoid header recursion hell 42 */ 43 #define init_task_preempt_count(p) do { } while (0) 44 45 #define init_idle_preempt_count(p, cpu) do { \ 46 per_cpu(__preempt_count, (cpu)) = PREEMPT_ENABLED; \ 47 } while (0) 48 49 /* 50 * We fold the NEED_RESCHED bit into the preempt count such that 51 * preempt_enable() can decrement and test for needing to reschedule with a 52 * single instruction. 53 * 54 * We invert the actual bit, so that when the decrement hits 0 we know we both 55 * need to resched (the bit is cleared) and can resched (no preempt count). 56 */ 57 58 static __always_inline void set_preempt_need_resched(void) 59 { 60 raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED); 61 } 62 63 static __always_inline void clear_preempt_need_resched(void) 64 { 65 raw_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED); 66 } 67 68 static __always_inline bool test_preempt_need_resched(void) 69 { 70 return !(raw_cpu_read_4(__preempt_count) & PREEMPT_NEED_RESCHED); 71 } 72 73 /* 74 * The various preempt_count add/sub methods 75 */ 76 77 static __always_inline void __preempt_count_add(int val) 78 { 79 raw_cpu_add_4(__preempt_count, val); 80 } 81 82 static __always_inline void __preempt_count_sub(int val) 83 { 84 raw_cpu_add_4(__preempt_count, -val); 85 } 86 87 /* 88 * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule 89 * a decrement which hits zero means we have no preempt_count and should 90 * reschedule. 91 */ 92 static __always_inline bool __preempt_count_dec_and_test(void) 93 { 94 return GEN_UNARY_RMWcc("decl", __preempt_count, e, __percpu_arg([var])); 95 } 96 97 /* 98 * Returns true when we need to resched and can (barring IRQ state). 99 */ 100 static __always_inline bool should_resched(int preempt_offset) 101 { 102 return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset); 103 } 104 105 #ifdef CONFIG_PREEMPTION 106 extern asmlinkage void preempt_schedule_thunk(void); 107 # define __preempt_schedule() \ 108 asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT) 109 110 extern asmlinkage void preempt_schedule(void); 111 extern asmlinkage void preempt_schedule_notrace_thunk(void); 112 # define __preempt_schedule_notrace() \ 113 asm volatile ("call preempt_schedule_notrace_thunk" : ASM_CALL_CONSTRAINT) 114 115 extern asmlinkage void preempt_schedule_notrace(void); 116 #endif 117 118 #endif /* __ASM_PREEMPT_H */ 119