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
   9DECLARE_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 */
  24static __always_inline int preempt_count(void)
  25{
  26        return raw_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
  27}
  28
  29static __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
  58static __always_inline void set_preempt_need_resched(void)
  59{
  60        raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
  61}
  62
  63static __always_inline void clear_preempt_need_resched(void)
  64{
  65        raw_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
  66}
  67
  68static __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
  77static __always_inline void __preempt_count_add(int val)
  78{
  79        raw_cpu_add_4(__preempt_count, val);
  80}
  81
  82static __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 */
  92static __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 */
 100static __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_PREEMPT
 106  extern asmlinkage void ___preempt_schedule(void);
 107# define __preempt_schedule() \
 108        asm volatile ("call ___preempt_schedule" : ASM_CALL_CONSTRAINT)
 109
 110  extern asmlinkage void preempt_schedule(void);
 111  extern asmlinkage void ___preempt_schedule_notrace(void);
 112# define __preempt_schedule_notrace() \
 113        asm volatile ("call ___preempt_schedule_notrace" : ASM_CALL_CONSTRAINT)
 114
 115  extern asmlinkage void preempt_schedule_notrace(void);
 116#endif
 117
 118#endif /* __ASM_PREEMPT_H */
 119