arch/i386/lib/dec_and_lock.c

   1 /*
   2  * x86 version of "atomic_dec_and_lock()" using
   3  * the atomic "cmpxchg" instruction.
   4  *
   5  * (For CPU's lacking cmpxchg, we use the slow
   6  * generic version, and this one never even gets
   7  * compiled).
   8  */
   9
  10 #include <linux/spinlock.h>
  11 #include <linux/module.h>
  12 #include <asm/atomic.h>
  13
  14 int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
  15 {
  16         int counter;
  17         int newcount;
  18
  19 repeat:
  20         counter = atomic_read(atomic);
  21         newcount = counter-1;
  22
  23         if (!newcount)
  24                 goto slow_path;
  25
  26         asm volatile("lock; cmpxchgl %1,%2"
  27                 :"=a" (newcount)
  28                 :"r" (newcount), "m" (atomic->counter), "0" (counter));
  29
  30         /* If the above failed, "eax" will have changed */
  31         if (newcount != counter)
  32                 goto repeat;
  33         return 0;
  34
  35 slow_path:
  36         spin_lock(lock);
  37         if (atomic_dec_and_test(atomic))
  38                 return 1;
  39         spin_unlock(lock);
  40         return 0;
  41 }
  42 EXPORT_SYMBOL(_atomic_dec_and_lock);