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