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
37extern void lockref_get(struct lockref *);
38extern int lockref_put_return(struct lockref *);
39extern int lockref_get_not_zero(struct lockref *);
40extern int lockref_put_not_zero(struct lockref *);
41extern int lockref_get_or_lock(struct lockref *);
42extern int lockref_put_or_lock(struct lockref *);
43
44extern void lockref_mark_dead(struct lockref *);
45extern int lockref_get_not_dead(struct lockref *);
46
47/* Must be called under spinlock for reliable results */
48static inline bool __lockref_is_dead(const struct lockref *l)
49{
50 return ((int)l->count < 0);
51}
52
53#endif /* __LINUX_LOCKREF_H */
54