1 #include <linux/module.h> 2 #include <linux/spinlock.h> 3 #include <asm/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 */ _atomic_dec_and_lock(atomic_t * atomic,spinlock_t * lock)20int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) 21 { 22 #ifdef CONFIG_SMP 23 /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */ 24 if (atomic_add_unless(atomic, -1, 1)) 25 return 0; 26 #endif 27 /* Otherwise do it the slow way */ 28 spin_lock(lock); 29 if (atomic_dec_and_test(atomic)) 30 return 1; 31 spin_unlock(lock); 32 return 0; 33 } 34 35 EXPORT_SYMBOL(_atomic_dec_and_lock); 36