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1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef __LINUX_LOCKREF_H
3#define __LINUX_LOCKREF_H
4
5/*
6 * Locked reference counts.
7 *
8 * These are different from just plain atomic refcounts in that they
9 * are atomic with respect to the spinlock that goes with them. In
10 * particular, there can be implementations that don't actually get
11 * the spinlock for the common decrement/increment operations, but they
12 * still have to check that the operation is done semantically as if
13 * the spinlock had been taken (using a cmpxchg operation that covers
14 * both the lock and the count word, or using memory transactions, for
15 * example).
16 */
17
18#include <linux/spinlock.h>
19#include <generated/bounds.h>
20
21#define USE_CMPXCHG_LOCKREF \
22 (IS_ENABLED(CONFIG_ARCH_USE_CMPXCHG_LOCKREF) && \
23 IS_ENABLED(CONFIG_SMP) && SPINLOCK_SIZE <= 4)
24
25struct lockref {
26 union {
27#if USE_CMPXCHG_LOCKREF
28 aligned_u64 lock_count;
29#endif
30 struct {
31 spinlock_t lock;
32 int count;
33 };
34 };
35};
36
37/**
38 * lockref_init - Initialize a lockref
39 * @lockref: pointer to lockref structure
40 *
41 * Initializes @lockref->count to 1.
42 */
43static inline void lockref_init(struct lockref *lockref)
44{
45 spin_lock_init(&lockref->lock);
46 lockref->count = 1;
47}
48
49void lockref_get(struct lockref *lockref);
50int lockref_put_return(struct lockref *lockref);
51bool lockref_get_not_zero(struct lockref *lockref);
52bool lockref_put_or_lock(struct lockref *lockref);
53
54void lockref_mark_dead(struct lockref *lockref);
55bool lockref_get_not_dead(struct lockref *lockref);
56
57/* Must be called under spinlock for reliable results */
58static inline bool __lockref_is_dead(const struct lockref *l)
59{
60 return ((int)l->count < 0);
61}
62
63#endif /* __LINUX_LOCKREF_H */