1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __ASM_PREEMPT_H
3 #define __ASM_PREEMPT_H
4
5 #include <asm/current.h>
6 #include <linux/thread_info.h>
7 #include <asm/atomic_ops.h>
8 #include <asm/cmpxchg.h>
9 #include <asm/march.h>
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 */
preempt_count(void)24 static __always_inline int preempt_count(void)
25 {
26 return READ_ONCE(get_lowcore()->preempt_count) & ~PREEMPT_NEED_RESCHED;
27 }
28
preempt_count_set(int pc)29 static __always_inline void preempt_count_set(int pc)
30 {
31 int old, new;
32
33 old = READ_ONCE(get_lowcore()->preempt_count);
34 do {
35 new = (old & PREEMPT_NEED_RESCHED) | (pc & ~PREEMPT_NEED_RESCHED);
36 } while (!arch_try_cmpxchg(&get_lowcore()->preempt_count, &old, new));
37 }
38
39 /*
40 * We fold the NEED_RESCHED bit into the preempt count such that
41 * preempt_enable() can decrement and test for needing to reschedule with a
42 * short instruction sequence.
43 *
44 * We invert the actual bit, so that when the decrement hits 0 we know we both
45 * need to resched (the bit is cleared) and can resched (no preempt count).
46 */
47
set_preempt_need_resched(void)48 static __always_inline void set_preempt_need_resched(void)
49 {
50 __atomic_and(~PREEMPT_NEED_RESCHED, &get_lowcore()->preempt_count);
51 }
52
clear_preempt_need_resched(void)53 static __always_inline void clear_preempt_need_resched(void)
54 {
55 __atomic_or(PREEMPT_NEED_RESCHED, &get_lowcore()->preempt_count);
56 }
57
test_preempt_need_resched(void)58 static __always_inline bool test_preempt_need_resched(void)
59 {
60 return !(READ_ONCE(get_lowcore()->preempt_count) & PREEMPT_NEED_RESCHED);
61 }
62
__preempt_count_add(int val)63 static __always_inline void __preempt_count_add(int val)
64 {
65 /*
66 * With some obscure config options and CONFIG_PROFILE_ALL_BRANCHES
67 * enabled, gcc 12 fails to handle __builtin_constant_p().
68 */
69 if (!IS_ENABLED(CONFIG_PROFILE_ALL_BRANCHES)) {
70 if (__builtin_constant_p(val) && (val >= -128) && (val <= 127)) {
71 __atomic_add_const(val, &get_lowcore()->preempt_count);
72 return;
73 }
74 }
75 __atomic_add(val, &get_lowcore()->preempt_count);
76 }
77
__preempt_count_sub(int val)78 static __always_inline void __preempt_count_sub(int val)
79 {
80 __preempt_count_add(-val);
81 }
82
83 /*
84 * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
85 * a decrement which hits zero means we have no preempt_count and should
86 * reschedule.
87 */
__preempt_count_dec_and_test(void)88 static __always_inline bool __preempt_count_dec_and_test(void)
89 {
90 return __atomic_add_const_and_test(-1, &get_lowcore()->preempt_count);
91 }
92
93 /*
94 * Returns true when we need to resched and can (barring IRQ state).
95 */
should_resched(int preempt_offset)96 static __always_inline bool should_resched(int preempt_offset)
97 {
98 return unlikely(READ_ONCE(get_lowcore()->preempt_count) == preempt_offset);
99 }
100
101 #define init_task_preempt_count(p) do { } while (0)
102 /* Deferred to CPU bringup time */
103 #define init_idle_preempt_count(p, cpu) do { } while (0)
104
105 #ifdef CONFIG_PREEMPTION
106
107 void preempt_schedule(void);
108 void preempt_schedule_notrace(void);
109
110 #ifdef CONFIG_PREEMPT_DYNAMIC
111
112 void dynamic_preempt_schedule(void);
113 void dynamic_preempt_schedule_notrace(void);
114 #define __preempt_schedule() dynamic_preempt_schedule()
115 #define __preempt_schedule_notrace() dynamic_preempt_schedule_notrace()
116
117 #else /* CONFIG_PREEMPT_DYNAMIC */
118
119 #define __preempt_schedule() preempt_schedule()
120 #define __preempt_schedule_notrace() preempt_schedule_notrace()
121
122 #endif /* CONFIG_PREEMPT_DYNAMIC */
123
124 #endif /* CONFIG_PREEMPTION */
125
126 #endif /* __ASM_PREEMPT_H */
127