1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Out-of-line refcount functions.
4 */
5
6#include <linux/mutex.h>
7#include <linux/refcount.h>
8#include <linux/spinlock.h>
9#include <linux/bug.h>
10
11#define REFCOUNT_WARN(str)	WARN_ONCE(1, "refcount_t: " str ".\n")
12
13void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t)
14{
15	refcount_set(r, REFCOUNT_SATURATED);
16
17	switch (t) {
18	case REFCOUNT_ADD_NOT_ZERO_OVF:
19		REFCOUNT_WARN("saturated; leaking memory");
20		break;
21	case REFCOUNT_ADD_OVF:
22		REFCOUNT_WARN("saturated; leaking memory");
23		break;
24	case REFCOUNT_ADD_UAF:
25		REFCOUNT_WARN("addition on 0; use-after-free");
26		break;
27	case REFCOUNT_SUB_UAF:
28		REFCOUNT_WARN("underflow; use-after-free");
29		break;
30	case REFCOUNT_DEC_LEAK:
31		REFCOUNT_WARN("decrement hit 0; leaking memory");
32		break;
33	default:
34		REFCOUNT_WARN("unknown saturation event!?");
35	}
36}
37EXPORT_SYMBOL(refcount_warn_saturate);
38
39/**
40 * refcount_dec_if_one - decrement a refcount if it is 1
41 * @r: the refcount
42 *
43 * No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the
44 * success thereof.
45 *
46 * Like all decrement operations, it provides release memory order and provides
47 * a control dependency.
48 *
49 * It can be used like a try-delete operator; this explicit case is provided
50 * and not cmpxchg in generic, because that would allow implementing unsafe
51 * operations.
52 *
53 * Return: true if the resulting refcount is 0, false otherwise
54 */
55bool refcount_dec_if_one(refcount_t *r)
56{
57	int val = 1;
58
59	return atomic_try_cmpxchg_release(&r->refs, &val, 0);
60}
61EXPORT_SYMBOL(refcount_dec_if_one);
62
63/**
64 * refcount_dec_not_one - decrement a refcount if it is not 1
65 * @r: the refcount
66 *
67 * No atomic_t counterpart, it decrements unless the value is 1, in which case
68 * it will return false.
69 *
70 * Was often done like: atomic_add_unless(&var, -1, 1)
71 *
72 * Return: true if the decrement operation was successful, false otherwise
73 */
74bool refcount_dec_not_one(refcount_t *r)
75{
76	unsigned int new, val = atomic_read(&r->refs);
77
78	do {
79		if (unlikely(val == REFCOUNT_SATURATED))
80			return true;
81
82		if (val == 1)
83			return false;
84
85		new = val - 1;
86		if (new > val) {
87			WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n");
88			return true;
89		}
90
91	} while (!atomic_try_cmpxchg_release(&r->refs, &val, new));
92
93	return true;
94}
95EXPORT_SYMBOL(refcount_dec_not_one);
96
97/**
98 * refcount_dec_and_mutex_lock - return holding mutex if able to decrement
99 *                               refcount to 0
100 * @r: the refcount
101 * @lock: the mutex to be locked
102 *
103 * Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
104 * to decrement when saturated at REFCOUNT_SATURATED.
105 *
106 * Provides release memory ordering, such that prior loads and stores are done
107 * before, and provides a control dependency such that free() must come after.
108 * See the comment on top.
109 *
110 * Return: true and hold mutex if able to decrement refcount to 0, false
111 *         otherwise
112 */
113bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
114{
115	if (refcount_dec_not_one(r))
116		return false;
117
118	mutex_lock(lock);
119	if (!refcount_dec_and_test(r)) {
120		mutex_unlock(lock);
121		return false;
122	}
123
124	return true;
125}
126EXPORT_SYMBOL(refcount_dec_and_mutex_lock);
127
128/**
129 * refcount_dec_and_lock - return holding spinlock if able to decrement
130 *                         refcount to 0
131 * @r: the refcount
132 * @lock: the spinlock to be locked
133 *
134 * Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
135 * decrement when saturated at REFCOUNT_SATURATED.
136 *
137 * Provides release memory ordering, such that prior loads and stores are done
138 * before, and provides a control dependency such that free() must come after.
139 * See the comment on top.
140 *
141 * Return: true and hold spinlock if able to decrement refcount to 0, false
142 *         otherwise
143 */
144bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
145{
146	if (refcount_dec_not_one(r))
147		return false;
148
149	spin_lock(lock);
150	if (!refcount_dec_and_test(r)) {
151		spin_unlock(lock);
152		return false;
153	}
154
155	return true;
156}
157EXPORT_SYMBOL(refcount_dec_and_lock);
158
159/**
160 * refcount_dec_and_lock_irqsave - return holding spinlock with disabled
161 *                                 interrupts if able to decrement refcount to 0
162 * @r: the refcount
163 * @lock: the spinlock to be locked
164 * @flags: saved IRQ-flags if the is acquired
165 *
166 * Same as refcount_dec_and_lock() above except that the spinlock is acquired
167 * with disabled interrupts.
168 *
169 * Return: true and hold spinlock if able to decrement refcount to 0, false
170 *         otherwise
171 */
172bool refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock,
173				   unsigned long *flags)
174{
175	if (refcount_dec_not_one(r))
176		return false;
177
178	spin_lock_irqsave(lock, *flags);
179	if (!refcount_dec_and_test(r)) {
180		spin_unlock_irqrestore(lock, *flags);
181		return false;
182	}
183
184	return true;
185}
186EXPORT_SYMBOL(refcount_dec_and_lock_irqsave);
187