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 int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
  16 {
  17         int counter;
  18         int newcount;
  19
  20         for (;;) {
  21                 counter = atomic_read(atomic);
  22                 newcount = counter - 1;
  23                 if (!newcount)
  24                         break;          /* do it the slow way */
  25
  26                 newcount = cmpxchg(&atomic->counter, counter, newcount);
  27                 if (newcount == counter)
  28                         return 0;
  29         }
  30
  31         spin_lock(lock);
  32         if (atomic_dec_and_test(atomic))
  33                 return 1;
  34         spin_unlock(lock);
  35         return 0;
  36 }
  37
  38 EXPORT_SYMBOL(_atomic_dec_and_lock);