arch/ppc/lib/dec_and_lock.c

   1 #include <linux/module.h>
   2 #include <linux/spinlock.h>
   3 #include <asm/atomic.h>
   4 #include <asm/system.h>
   5
   6 /*
   7  * This is an implementation of the notion of "decrement a
   8  * reference count, and return locked if it decremented to zero".
   9  *
  10  * This implementation can be used on any architecture that
  11  * has a cmpxchg, and where atomic->value is an int holding
  12  * the value of the atomic (i.e. the high bits aren't used
  13  * for a lock or anything like that).
  14  *
  15  * N.B. ATOMIC_DEC_AND_LOCK gets defined in include/linux/spinlock.h
  16  * if spinlocks are empty and thus atomic_dec_and_lock is defined
  17  * to be atomic_dec_and_test - in that case we don't need it
  18  * defined here as well.
  19  */
  20
  21 #ifndef ATOMIC_DEC_AND_LOCK
  22 int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
  23 {
  24         int counter;
  25         int newcount;
  26
  27         for (;;) {
  28                 counter = atomic_read(atomic);
  29                 newcount = counter - 1;
  30                 if (!newcount)
  31                         break;          /* do it the slow way */
  32
  33                 newcount = cmpxchg(&atomic->counter, counter, newcount);
  34                 if (newcount == counter)
  35                         return 0;
  36         }
  37
  38         spin_lock(lock);
  39         if (atomic_dec_and_test(atomic))
  40                 return 1;
  41         spin_unlock(lock);
  42         return 0;
  43 }
  44
  45 EXPORT_SYMBOL(_atomic_dec_and_lock);
  46 #endif /* ATOMIC_DEC_AND_LOCK */