Line data    Source code

       1             : // SPDX-License-Identifier: GPL-2.0
       2             : #include <linux/export.h>
       3             : #include <linux/spinlock.h>
       4             : #include <linux/atomic.h>
       5             : 
       6             : /*
       7             :  * This is an implementation of the notion of "decrement a
       8             :  * reference count, and return locked if it decremented to zero".
       9             :  *
      10             :  * NOTE NOTE NOTE! This is _not_ equivalent to
      11             :  *
      12             :  *      if (atomic_dec_and_test(&atomic)) {
      13             :  *              spin_lock(&lock);
      14             :  *              return 1;
      15             :  *      }
      16             :  *      return 0;
      17             :  *
      18             :  * because the spin-lock and the decrement must be
      19             :  * "atomic".
      20             :  */
      21        7545 : int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
      22             : {
      23             :         /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
      24       15090 :         if (atomic_add_unless(atomic, -1, 1))
      25             :                 return 0;
      26             : 
      27             :         /* Otherwise do it the slow way */
      28        5723 :         spin_lock(lock);
      29       11448 :         if (atomic_dec_and_test(atomic))
      30             :                 return 1;
      31           0 :         spin_unlock(lock);
      32           0 :         return 0;
      33             : }
      34             : 
      35             : EXPORT_SYMBOL(_atomic_dec_and_lock);
      36             : 
      37           0 : int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,
      38             :                                  unsigned long *flags)
      39             : {
      40             :         /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
      41           0 :         if (atomic_add_unless(atomic, -1, 1))
      42             :                 return 0;
      43             : 
      44             :         /* Otherwise do it the slow way */
      45           0 :         spin_lock_irqsave(lock, *flags);
      46           0 :         if (atomic_dec_and_test(atomic))
      47             :                 return 1;
      48           0 :         spin_unlock_irqrestore(lock, *flags);
      49           0 :         return 0;
      50             : }
      51             : EXPORT_SYMBOL(_atomic_dec_and_lock_irqsave);