arch/ppc64/lib/dec_and_lock.c

   1 /*
   2  * ppc64 version of atomic_dec_and_lock() using cmpxchg
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version
   7  * 2 of the License, or (at your option) any later version.
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/spinlock.h>
  12 #include <asm/atomic.h>
  13 #include <asm/system.h>
  14
  15 /*
  16  * This is an implementation of the notion of "decrement a
  17  * reference count, and return locked if it decremented to zero".
  18  *
  19  * This implementation can be used on any architecture that
  20  * has a cmpxchg, and where atomic->value is an int holding
  21  * the value of the atomic (i.e. the high bits aren't used
  22  * for a lock or anything like that).
  23  */
  24 int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
  25 {
  26         int counter;
  27         int newcount;
  28
  29         for (;;) {
  30                 counter = atomic_read(atomic);
  31                 newcount = counter - 1;
  32                 if (!newcount)
  33                         break;          /* do it the slow way */
  34
  35                 newcount = cmpxchg(&atomic->counter, counter, newcount);
  36                 if (newcount == counter)
  37                         return 0;
  38         }
  39
  40         spin_lock(lock);
  41         if (atomic_dec_and_test(atomic))
  42                 return 1;
  43         spin_unlock(lock);
  44         return 0;
  45 }
  46
  47 EXPORT_SYMBOL(_atomic_dec_and_lock);