Line data    Source code

       1             : #include <linux/export.h>
       2             : #include <linux/spinlock.h>
       3             : #include <linux/atomic.h>
       4             : 
       5             : /*
       6             :  * This is an implementation of the notion of "decrement a
       7             :  * reference count, and return locked if it decremented to zero".
       8             :  *
       9             :  * NOTE NOTE NOTE! This is _not_ equivalent to
      10             :  *
      11             :  *      if (atomic_dec_and_test(&atomic)) {
      12             :  *              spin_lock(&lock);
      13             :  *              return 1;
      14             :  *      }
      15             :  *      return 0;
      16             :  *
      17             :  * because the spin-lock and the decrement must be
      18             :  * "atomic".
      19             :  */
      20       40906 : int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
      21             : {
      22             :         /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
      23       40906 :         if (atomic_add_unless(atomic, -1, 1))
      24             :                 return 0;
      25             : 
      26             :         /* Otherwise do it the slow way */
      27             :         spin_lock(lock);
      28       12342 :         if (atomic_dec_and_test(atomic))
      29             :                 return 1;
      30             :         spin_unlock(lock);
      31             :         return 0;
      32             : }
      33             : 
      34             : EXPORT_SYMBOL(_atomic_dec_and_lock);