xref: /openbmc/linux/lib/dec_and_lock.c (revision 4f64a6c9)
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  */
_atomic_dec_and_lock(atomic_t * atomic,spinlock_t * lock)21 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 	if (atomic_add_unless(atomic, -1, 1))
25 		return 0;
26 
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 
_atomic_dec_and_lock_irqsave(atomic_t * atomic,spinlock_t * lock,unsigned long * flags)37 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 	if (atomic_add_unless(atomic, -1, 1))
42 		return 0;
43 
44 	/* Otherwise do it the slow way */
45 	spin_lock_irqsave(lock, *flags);
46 	if (atomic_dec_and_test(atomic))
47 		return 1;
48 	spin_unlock_irqrestore(lock, *flags);
49 	return 0;
50 }
51 EXPORT_SYMBOL(_atomic_dec_and_lock_irqsave);
52 
_atomic_dec_and_raw_lock(atomic_t * atomic,raw_spinlock_t * lock)53 int _atomic_dec_and_raw_lock(atomic_t *atomic, raw_spinlock_t *lock)
54 {
55 	/* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
56 	if (atomic_add_unless(atomic, -1, 1))
57 		return 0;
58 
59 	/* Otherwise do it the slow way */
60 	raw_spin_lock(lock);
61 	if (atomic_dec_and_test(atomic))
62 		return 1;
63 	raw_spin_unlock(lock);
64 	return 0;
65 }
66 EXPORT_SYMBOL(_atomic_dec_and_raw_lock);
67 
_atomic_dec_and_raw_lock_irqsave(atomic_t * atomic,raw_spinlock_t * lock,unsigned long * flags)68 int _atomic_dec_and_raw_lock_irqsave(atomic_t *atomic, raw_spinlock_t *lock,
69 				     unsigned long *flags)
70 {
71 	/* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
72 	if (atomic_add_unless(atomic, -1, 1))
73 		return 0;
74 
75 	/* Otherwise do it the slow way */
76 	raw_spin_lock_irqsave(lock, *flags);
77 	if (atomic_dec_and_test(atomic))
78 		return 1;
79 	raw_spin_unlock_irqrestore(lock, *flags);
80 	return 0;
81 }
82 EXPORT_SYMBOL(_atomic_dec_and_raw_lock_irqsave);
83