include/linux/bit_spinlock.h

   1 #ifndef __LINUX_BIT_SPINLOCK_H
   2 #define __LINUX_BIT_SPINLOCK_H
   3
   4 /*
   5  *  bit-based spin_lock()
   6  *
   7  * Don't use this unless you really need to: spin_lock() and spin_unlock()
   8  * are significantly faster.
   9  */
  10 static inline void bit_spin_lock(int bitnum, unsigned long *addr)
  11 {
  12         /*
  13          * Assuming the lock is uncontended, this never enters
  14          * the body of the outer loop. If it is contended, then
  15          * within the inner loop a non-atomic test is used to
  16          * busywait with less bus contention for a good time to
  17          * attempt to acquire the lock bit.
  18          */
  19         preempt_disable();
  20 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  21         while (test_and_set_bit(bitnum, addr)) {
  22                 while (test_bit(bitnum, addr)) {
  23                         preempt_enable();
  24                         cpu_relax();
  25                         preempt_disable();
  26                 }
  27         }
  28 #endif
  29         __acquire(bitlock);
  30 }
  31
  32 /*
  33  * Return true if it was acquired
  34  */
  35 static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
  36 {
  37         preempt_disable();
  38 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  39         if (test_and_set_bit(bitnum, addr)) {
  40                 preempt_enable();
  41                 return 0;
  42         }
  43 #endif
  44         __acquire(bitlock);
  45         return 1;
  46 }
  47
  48 /*
  49  *  bit-based spin_unlock()
  50  */
  51 static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
  52 {
  53 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  54         BUG_ON(!test_bit(bitnum, addr));
  55         smp_mb__before_clear_bit();
  56         clear_bit(bitnum, addr);
  57 #endif
  58         preempt_enable();
  59         __release(bitlock);
  60 }
  61
  62 /*
  63  * Return true if the lock is held.
  64  */
  65 static inline int bit_spin_is_locked(int bitnum, unsigned long *addr)
  66 {
  67 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
  68         return test_bit(bitnum, addr);
  69 #elif defined CONFIG_PREEMPT
  70         return preempt_count();
  71 #else
  72         return 1;
  73 #endif
  74 }
  75
  76 #endif /* __LINUX_BIT_SPINLOCK_H */
  77