include/linux/bit_spinlock.h

   1 #ifndef __LINUX_BIT_SPINLOCK_H
   2 #define __LINUX_BIT_SPINLOCK_H
   3
   4 #include <linux/kernel.h>
   5 #include <linux/preempt.h>
   6 #include <asm/atomic.h>
   7
   8 /*
   9  *  bit-based spin_lock()
  10  *
  11  * Don't use this unless you really need to: spin_lock() and spin_unlock()
  12  * are significantly faster.
  13  */
  14 static inline void bit_spin_lock(int bitnum, unsigned long *addr)
  15 {
  16         /*
  17          * Assuming the lock is uncontended, this never enters
  18          * the body of the outer loop. If it is contended, then
  19          * within the inner loop a non-atomic test is used to
  20          * busywait with less bus contention for a good time to
  21          * attempt to acquire the lock bit.
  22          */
  23         preempt_disable();
  24 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  25         while (unlikely(test_and_set_bit_lock(bitnum, addr))) {
  26                 while (test_bit(bitnum, addr)) {
  27                         preempt_enable();
  28                         cpu_relax();
  29                         preempt_disable();
  30                 }
  31         }
  32 #endif
  33         __acquire(bitlock);
  34 }
  35
  36 /*
  37  * Return true if it was acquired
  38  */
  39 static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
  40 {
  41         preempt_disable();
  42 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  43         if (unlikely(test_and_set_bit_lock(bitnum, addr))) {
  44                 preempt_enable();
  45                 return 0;
  46         }
  47 #endif
  48         __acquire(bitlock);
  49         return 1;
  50 }
  51
  52 /*
  53  *  bit-based spin_unlock()
  54  */
  55 static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
  56 {
  57 #ifdef CONFIG_DEBUG_SPINLOCK
  58         BUG_ON(!test_bit(bitnum, addr));
  59 #endif
  60 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  61         clear_bit_unlock(bitnum, addr);
  62 #endif
  63         preempt_enable();
  64         __release(bitlock);
  65 }
  66
  67 /*
  68  *  bit-based spin_unlock()
  69  *  non-atomic version, which can be used eg. if the bit lock itself is
  70  *  protecting the rest of the flags in the word.
  71  */
  72 static inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
  73 {
  74 #ifdef CONFIG_DEBUG_SPINLOCK
  75         BUG_ON(!test_bit(bitnum, addr));
  76 #endif
  77 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  78         __clear_bit_unlock(bitnum, addr);
  79 #endif
  80         preempt_enable();
  81         __release(bitlock);
  82 }
  83
  84 /*
  85  * Return true if the lock is held.
  86  */
  87 static inline int bit_spin_is_locked(int bitnum, unsigned long *addr)
  88 {
  89 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  90         return test_bit(bitnum, addr);
  91 #elif defined CONFIG_PREEMPT
  92         return preempt_count();
  93 #else
  94         return 1;
  95 #endif
  96 }
  97
  98 #endif /* __LINUX_BIT_SPINLOCK_H */
  99