LXR linux/arch/x86/include/asm/preempt.h

   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#include <linux/static_call_types.h>
   9
  10DECLARE_PER_CPU(int, __preempt_count);
  11
  12/* We use the MSB mostly because its available */
  13#define PREEMPT_NEED_RESCHED    0x80000000
  14
  15/*
  16 * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such
  17 * that a decrement hitting 0 means we can and should reschedule.
  18 */
  19#define PREEMPT_ENABLED (0 + PREEMPT_NEED_RESCHED)
  20
  21/*
  22 * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
  23 * that think a non-zero value indicates we cannot preempt.
  24 */
  25static __always_inline int preempt_count(void)
  26{
  27        return raw_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
  28}
  29
  30static __always_inline void preempt_count_set(int pc)
  31{
  32        int old, new;
  33
  34        do {
  35                old = raw_cpu_read_4(__preempt_count);
  36                new = (old & PREEMPT_NEED_RESCHED) |
  37                        (pc & ~PREEMPT_NEED_RESCHED);
  38        } while (raw_cpu_cmpxchg_4(__preempt_count, old, new) != old);
  39}
  40
  41/*
  42 * must be macros to avoid header recursion hell
  43 */
  44#define init_task_preempt_count(p) do { } while (0)
  45
  46#define init_idle_preempt_count(p, cpu) do { \
  47        per_cpu(__preempt_count, (cpu)) = PREEMPT_DISABLED; \
  48} while (0)
  49
  50/*
  51 * We fold the NEED_RESCHED bit into the preempt count such that
  52 * preempt_enable() can decrement and test for needing to reschedule with a
  53 * single instruction.
  54 *
  55 * We invert the actual bit, so that when the decrement hits 0 we know we both
  56 * need to resched (the bit is cleared) and can resched (no preempt count).
  57 */
  58
  59static __always_inline void set_preempt_need_resched(void)
  60{
  61        raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
  62}
  63
  64static __always_inline void clear_preempt_need_resched(void)
  65{
  66        raw_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
  67}
  68
  69static __always_inline bool test_preempt_need_resched(void)
  70{
  71        return !(raw_cpu_read_4(__preempt_count) & PREEMPT_NEED_RESCHED);
  72}
  73
  74/*
  75 * The various preempt_count add/sub methods
  76 */
  77
  78static __always_inline void __preempt_count_add(int val)
  79{
  80        raw_cpu_add_4(__preempt_count, val);
  81}
  82
  83static __always_inline void __preempt_count_sub(int val)
  84{
  85        raw_cpu_add_4(__preempt_count, -val);
  86}
  87
  88/*
  89 * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
  90 * a decrement which hits zero means we have no preempt_count and should
  91 * reschedule.
  92 */
  93static __always_inline bool __preempt_count_dec_and_test(void)
  94{
  95        return GEN_UNARY_RMWcc("decl", __preempt_count, e, __percpu_arg([var]));
  96}
  97
  98/*
  99 * Returns true when we need to resched and can (barring IRQ state).
 100 */
 101static __always_inline bool should_resched(int preempt_offset)
 102{
 103        return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
 104}
 105
 106#ifdef CONFIG_PREEMPTION
 107
 108extern asmlinkage void preempt_schedule(void);
 109extern asmlinkage void preempt_schedule_thunk(void);
 110
 111#define __preempt_schedule_func preempt_schedule_thunk
 112
 113extern asmlinkage void preempt_schedule_notrace(void);
 114extern asmlinkage void preempt_schedule_notrace_thunk(void);
 115
 116#define __preempt_schedule_notrace_func preempt_schedule_notrace_thunk
 117
 118#ifdef CONFIG_PREEMPT_DYNAMIC
 119
 120DECLARE_STATIC_CALL(preempt_schedule, __preempt_schedule_func);
 121
 122#define __preempt_schedule() \
 123do { \
 124        __STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule); \
 125        asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \
 126} while (0)
 127
 128DECLARE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func);
 129
 130#define __preempt_schedule_notrace() \
 131do { \
 132        __STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule_notrace); \
 133        asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule_notrace) : ASM_CALL_CONSTRAINT); \
 134} while (0)
 135
 136#else /* PREEMPT_DYNAMIC */
 137
 138#define __preempt_schedule() \
 139        asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT);
 140
 141#define __preempt_schedule_notrace() \
 142        asm volatile ("call preempt_schedule_notrace_thunk" : ASM_CALL_CONSTRAINT);
 143
 144#endif /* PREEMPT_DYNAMIC */
 145
 146#endif /* PREEMPTION */
 147
 148#endif /* __ASM_PREEMPT_H */
 149