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 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 if (atomic_add_unless(atomic, -1, 1)) 24 return 0; 25 26 /* Otherwise do it the slow way */ 27 spin_lock(lock); 28 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); 35