include/asm-generic/preempt.h

   1 #ifndef __ASM_PREEMPT_H
   2 #define __ASM_PREEMPT_H
   3
   4 #include <linux/thread_info.h>
   5
   6 /*
   7  * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
   8  * that think a non-zero value indicates we cannot preempt.
   9  */
  10 static __always_inline int preempt_count(void)
  11 {
  12         return current_thread_info()->preempt_count & ~PREEMPT_NEED_RESCHED;
  13 }
  14
  15 static __always_inline int *preempt_count_ptr(void)
  16 {
  17         return &current_thread_info()->preempt_count;
  18 }
  19
  20 /*
  21  * We now loose PREEMPT_NEED_RESCHED and cause an extra reschedule; however the
  22  * alternative is loosing a reschedule. Better schedule too often -- also this
  23  * should be a very rare operation.
  24  */
  25 static __always_inline void preempt_count_set(int pc)
  26 {
  27         *preempt_count_ptr() = pc;
  28 }
  29
  30 /*
  31  * must be macros to avoid header recursion hell
  32  */
  33 #define task_preempt_count(p) \
  34         (task_thread_info(p)->preempt_count & ~PREEMPT_NEED_RESCHED)
  35
  36 #define init_task_preempt_count(p) do { \
  37         task_thread_info(p)->preempt_count = PREEMPT_DISABLED; \
  38 } while (0)
  39
  40 #define init_idle_preempt_count(p, cpu) do { \
  41         task_thread_info(p)->preempt_count = PREEMPT_ENABLED; \
  42 } while (0)
  43
  44 /*
  45  * We fold the NEED_RESCHED bit into the preempt count such that
  46  * preempt_enable() can decrement and test for needing to reschedule with a
  47  * single instruction.
  48  *
  49  * We invert the actual bit, so that when the decrement hits 0 we know we both
  50  * need to resched (the bit is cleared) and can resched (no preempt count).
  51  */
  52
  53 static __always_inline void set_preempt_need_resched(void)
  54 {
  55         *preempt_count_ptr() &= ~PREEMPT_NEED_RESCHED;
  56 }
  57
  58 static __always_inline void clear_preempt_need_resched(void)
  59 {
  60         *preempt_count_ptr() |= PREEMPT_NEED_RESCHED;
  61 }
  62
  63 static __always_inline bool test_preempt_need_resched(void)
  64 {
  65         return !(*preempt_count_ptr() & PREEMPT_NEED_RESCHED);
  66 }
  67
  68 /*
  69  * The various preempt_count add/sub methods
  70  */
  71
  72 static __always_inline void __preempt_count_add(int val)
  73 {
  74         *preempt_count_ptr() += val;
  75 }
  76
  77 static __always_inline void __preempt_count_sub(int val)
  78 {
  79         *preempt_count_ptr() -= val;
  80 }
  81
  82 static __always_inline bool __preempt_count_dec_and_test(void)
  83 {
  84         return !--*preempt_count_ptr();
  85 }
  86
  87 /*
  88  * Returns true when we need to resched and can (barring IRQ state).
  89  */
  90 static __always_inline bool should_resched(void)
  91 {
  92         return unlikely(!*preempt_count_ptr());
  93 }
  94
  95 #ifdef CONFIG_PREEMPT
  96 extern asmlinkage void preempt_schedule(void);
  97 #define __preempt_schedule() preempt_schedule()
  98
  99 #ifdef CONFIG_CONTEXT_TRACKING
 100 extern asmlinkage void preempt_schedule_context(void);
 101 #define __preempt_schedule_context() preempt_schedule_context()
 102 #endif
 103 #endif /* CONFIG_PREEMPT */
 104
 105 #endif /* __ASM_PREEMPT_H */