1 #include <linux/module.h>
2 #include <linux/spinlock.h>
3 #include <asm/atomic.h>
4 
5 /*
6  * This is an architecture-neutral, but slow,
7  * implementation of the notion of "decrement
8  * a reference count, and return locked if it
9  * decremented to zero".
10  *
11  * NOTE NOTE NOTE! This is _not_ equivalent to
12  *
13  *	if (atomic_dec_and_test(&atomic)) {
14  *		spin_lock(&lock);
15  *		return 1;
16  *	}
17  *	return 0;
18  *
19  * because the spin-lock and the decrement must be
20  * "atomic".
21  *
22  * This slow version gets the spinlock unconditionally,
23  * and releases it if it isn't needed. Architectures
24  * are encouraged to come up with better approaches,
25  * this is trivially done efficiently using a load-locked
26  * store-conditional approach, for example.
27  */
28 
29 #ifndef ATOMIC_DEC_AND_LOCK
atomic_dec_and_lock(atomic_t * atomic,spinlock_t * lock)30 int atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
31 {
32 	spin_lock(lock);
33 	if (atomic_dec_and_test(atomic))
34 		return 1;
35 	spin_unlock(lock);
36 	return 0;
37 }
38 
39 EXPORT_SYMBOL(atomic_dec_and_lock);
40 #endif
41