root/arch/x86/include/asm/preempt.h

INCLUDED FROM

DEFINITIONS

1. preempt_count
2. preempt_count_set
3. set_preempt_need_resched
4. clear_preempt_need_resched
5. test_preempt_need_resched
6. __preempt_count_add
7. __preempt_count_sub
8. __preempt_count_dec_and_test
9. should_resched

   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 /* 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(__preempt_count) & ~PREEMPT_NEED_RESCHED;
  27 }
  28 
  29 static __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 
  58 static __always_inline void set_preempt_need_resched(void)
  59 {
  60         raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
  61 }
  62 
  63 static __always_inline void clear_preempt_need_resched(void)
  64 {
  65         raw_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
  66 }
  67 
  68 static __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 
  77 static __always_inline void __preempt_count_add(int val)
  78 {
  79         raw_cpu_add_4(__preempt_count, val);
  80 }
  81 
  82 static __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  */
  92 static __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  */
 100 static __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_PREEMPTION
 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 */