arch/mips/lib/dec_and_lock.c

   1 /*
   2  * MIPS 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  * N.B. ATOMIC_DEC_AND_LOCK gets defined in include/linux/spinlock.h
  25  * if spinlocks are empty and thus atomic_dec_and_lock is defined
  26  * to be atomic_dec_and_test - in that case we don't need it
  27  * defined here as well.
  28  */
  29
  30 #ifndef ATOMIC_DEC_AND_LOCK
  31 int atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
  32 {
  33         int counter;
  34         int newcount;
  35
  36         for (;;) {
  37                 counter = atomic_read(atomic);
  38                 newcount = counter - 1;
  39                 if (!newcount)
  40                         break;          /* do it the slow way */
  41
  42                 newcount = cmpxchg(&atomic->counter, counter, newcount);
  43                 if (newcount == counter)
  44                         return 0;
  45         }
  46
  47         spin_lock(lock);
  48         if (atomic_dec_and_test(atomic))
  49                 return 1;
  50         spin_unlock(lock);
  51         return 0;
  52 }
  53
  54 EXPORT_SYMBOL(atomic_dec_and_lock);
  55 #endif /* ATOMIC_DEC_AND_LOCK */