lockref.h

 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#define lockref_put_or_lock(_lockref) \
54	(!__cond_lock((_lockref)->lock, !lockref_put_or_lock(_lockref)))
55
56void lockref_mark_dead(struct lockref *lockref);
57bool lockref_get_not_dead(struct lockref *lockref);
58
59/* Must be called under spinlock for reliable results */
60static inline bool __lockref_is_dead(const struct lockref *l)
61{
62	return ((int)l->count < 0);
63}
64
65#endif /* __LINUX_LOCKREF_H */