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 <asm/current.h>
8
9 #include <linux/static_call_types.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 */
24 static __always_inline int preempt_count(void)
25 {
26 return raw_cpu_read_4(pcpu_hot.preempt_count) & ~PREEMPT_NEED_RESCHED;
27 }
28
29 static __always_inline void preempt_count_set(int pc)
30 {
31 int old, new;
32
33 old = raw_cpu_read_4(pcpu_hot.preempt_count);
34 do {
35 new = (old & PREEMPT_NEED_RESCHED) |
36 (pc & ~PREEMPT_NEED_RESCHED);
37 } while (!raw_cpu_try_cmpxchg_4(pcpu_hot.preempt_count, &old, new));
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(pcpu_hot.preempt_count, (cpu)) = PREEMPT_DISABLED; \
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(pcpu_hot.preempt_count, ~PREEMPT_NEED_RESCHED);
61 }
62
63 static __always_inline void clear_preempt_need_resched(void)
64 {
65 raw_cpu_or_4(pcpu_hot.preempt_count, PREEMPT_NEED_RESCHED);
66 }
67
68 static __always_inline bool test_preempt_need_resched(void)
69 {
70 return !(raw_cpu_read_4(pcpu_hot.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(pcpu_hot.preempt_count, val);
80 }
81
82 static __always_inline void __preempt_count_sub(int val)
83 {
84 raw_cpu_add_4(pcpu_hot.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", __my_cpu_var(pcpu_hot.preempt_count), e,
95 __percpu_arg([var]));
96 }
97
98 /*
99 * Returns true when we need to resched and can (barring IRQ state).
100 */
101 static __always_inline bool should_resched(int preempt_offset)
102 {
103 return unlikely(raw_cpu_read_4(pcpu_hot.preempt_count) == preempt_offset);
104 }
105
106 #ifdef CONFIG_PREEMPTION
107
108 extern asmlinkage void preempt_schedule(void);
109 extern asmlinkage void preempt_schedule_thunk(void);
110
111 #define preempt_schedule_dynamic_enabled preempt_schedule_thunk
112 #define preempt_schedule_dynamic_disabled NULL
113
114 extern asmlinkage void preempt_schedule_notrace(void);
115 extern asmlinkage void preempt_schedule_notrace_thunk(void);
116
117 #define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace_thunk
118 #define preempt_schedule_notrace_dynamic_disabled NULL
119
120 #ifdef CONFIG_PREEMPT_DYNAMIC
121
122 DECLARE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
123
124 #define __preempt_schedule() \
125 do { \
126 __STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule); \
127 asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \
128 } while (0)
129
130 DECLARE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
131
132 #define __preempt_schedule_notrace() \
133 do { \
134 __STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule_notrace); \
135 asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule_notrace) : ASM_CALL_CONSTRAINT); \
136 } while (0)
137
138 #else /* PREEMPT_DYNAMIC */
139
140 #define __preempt_schedule() \
141 asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT);
142
143 #define __preempt_schedule_notrace() \
144 asm volatile ("call preempt_schedule_notrace_thunk" : ASM_CALL_CONSTRAINT);
145
146 #endif /* PREEMPT_DYNAMIC */
147
148 #endif /* PREEMPTION */
149
150 #endif /* __ASM_PREEMPT_H */
151
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