arch/ia64/lib/dec_and_lock.c

   1 /*
   2  * Copyright (C) 2003 Jerome Marchand, Bull S.A.
   3  *      Cleaned up by David Mosberger-Tang <davidm@hpl.hp.com>
   4  *
   5  * This file is released under the GPLv2, or at your option any later version.
   6  *
   7  * ia64 version of "atomic_dec_and_lock()" using the atomic "cmpxchg" instruction.  This
   8  * code is an adaptation of the x86 version of "atomic_dec_and_lock()".
   9  */
  10
  11 #include <linux/compiler.h>
  12 #include <linux/module.h>
  13 #include <linux/spinlock.h>
  14 #include <asm/atomic.h>
  15
  16 /*
  17  * Decrement REFCOUNT and if the count reaches zero, acquire the spinlock.  Both of these
  18  * operations have to be done atomically, so that the count doesn't drop to zero without
  19  * acquiring the spinlock first.
  20  */
  21 int
  22 _atomic_dec_and_lock (atomic_t *refcount, spinlock_t *lock)
  23 {
  24         int old, new;
  25
  26         do {
  27                 old = atomic_read(refcount);
  28                 new = old - 1;
  29
  30                 if (unlikely (old == 1)) {
  31                         /* oops, we may be decrementing to zero, do it the slow way... */
  32                         spin_lock(lock);
  33                         if (atomic_dec_and_test(refcount))
  34                                 return 1;
  35                         spin_unlock(lock);
  36                         return 0;
  37                 }
  38         } while (cmpxchg(&refcount->counter, old, new) != old);
  39         return 0;
  40 }
  41
  42 EXPORT_SYMBOL(_atomic_dec_and_lock);