1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0
2*4882a593Smuzhiyun #include <linux/export.h>
3*4882a593Smuzhiyun #include <linux/spinlock.h>
4*4882a593Smuzhiyun #include <linux/atomic.h>
5*4882a593Smuzhiyun
6*4882a593Smuzhiyun /*
7*4882a593Smuzhiyun * This is an implementation of the notion of "decrement a
8*4882a593Smuzhiyun * reference count, and return locked if it decremented to zero".
9*4882a593Smuzhiyun *
10*4882a593Smuzhiyun * NOTE NOTE NOTE! This is _not_ equivalent to
11*4882a593Smuzhiyun *
12*4882a593Smuzhiyun * if (atomic_dec_and_test(&atomic)) {
13*4882a593Smuzhiyun * spin_lock(&lock);
14*4882a593Smuzhiyun * return 1;
15*4882a593Smuzhiyun * }
16*4882a593Smuzhiyun * return 0;
17*4882a593Smuzhiyun *
18*4882a593Smuzhiyun * because the spin-lock and the decrement must be
19*4882a593Smuzhiyun * "atomic".
20*4882a593Smuzhiyun */
_atomic_dec_and_lock(atomic_t * atomic,spinlock_t * lock)21*4882a593Smuzhiyun int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
22*4882a593Smuzhiyun {
23*4882a593Smuzhiyun /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
24*4882a593Smuzhiyun if (atomic_add_unless(atomic, -1, 1))
25*4882a593Smuzhiyun return 0;
26*4882a593Smuzhiyun
27*4882a593Smuzhiyun /* Otherwise do it the slow way */
28*4882a593Smuzhiyun spin_lock(lock);
29*4882a593Smuzhiyun if (atomic_dec_and_test(atomic))
30*4882a593Smuzhiyun return 1;
31*4882a593Smuzhiyun spin_unlock(lock);
32*4882a593Smuzhiyun return 0;
33*4882a593Smuzhiyun }
34*4882a593Smuzhiyun
35*4882a593Smuzhiyun EXPORT_SYMBOL(_atomic_dec_and_lock);
36*4882a593Smuzhiyun
_atomic_dec_and_lock_irqsave(atomic_t * atomic,spinlock_t * lock,unsigned long * flags)37*4882a593Smuzhiyun int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,
38*4882a593Smuzhiyun unsigned long *flags)
39*4882a593Smuzhiyun {
40*4882a593Smuzhiyun /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
41*4882a593Smuzhiyun if (atomic_add_unless(atomic, -1, 1))
42*4882a593Smuzhiyun return 0;
43*4882a593Smuzhiyun
44*4882a593Smuzhiyun /* Otherwise do it the slow way */
45*4882a593Smuzhiyun spin_lock_irqsave(lock, *flags);
46*4882a593Smuzhiyun if (atomic_dec_and_test(atomic))
47*4882a593Smuzhiyun return 1;
48*4882a593Smuzhiyun spin_unlock_irqrestore(lock, *flags);
49*4882a593Smuzhiyun return 0;
50*4882a593Smuzhiyun }
51*4882a593Smuzhiyun EXPORT_SYMBOL(_atomic_dec_and_lock_irqsave);
52