2 * kref.h - library routines for handling generic reference counted objects
4 * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
5 * Copyright (C) 2004 IBM Corp.
7 * based on kobject.h which was:
8 * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
9 * Copyright (C) 2002-2003 Open Source Development Labs
11 * This file is released under the GPLv2.
18 #include <linux/bug.h>
19 #include <linux/atomic.h>
20 #include <linux/kernel.h>
21 #include <linux/mutex.h>
22 #include <linux/spinlock.h>
29 * kref_init - initialize object.
30 * @kref: object in question.
32 static inline void kref_init(struct kref
*kref
)
34 atomic_set(&kref
->refcount
, 1);
38 * kref_get - increment refcount for object.
41 static inline void kref_get(struct kref
*kref
)
43 /* If refcount was 0 before incrementing then we have a race
44 * condition when this kref is freeing by some other thread right now.
45 * In this case one should use kref_get_unless_zero()
47 WARN_ON_ONCE(atomic_inc_return(&kref
->refcount
) < 2);
51 * kref_sub - subtract a number of refcounts for object.
53 * @count: Number of recounts to subtract.
54 * @release: pointer to the function that will clean up the object when the
55 * last reference to the object is released.
56 * This pointer is required, and it is not acceptable to pass kfree
57 * in as this function. If the caller does pass kfree to this
58 * function, you will be publicly mocked mercilessly by the kref
59 * maintainer, and anyone else who happens to notice it. You have
62 * Subtract @count from the refcount, and if 0, call release().
63 * Return 1 if the object was removed, otherwise return 0. Beware, if this
64 * function returns 0, you still can not count on the kref from remaining in
65 * memory. Only use the return value if you want to see if the kref is now
68 static inline int kref_sub(struct kref
*kref
, unsigned int count
,
69 void (*release
)(struct kref
*kref
))
71 WARN_ON(release
== NULL
);
73 if (atomic_sub_and_test((int) count
, &kref
->refcount
)) {
81 * kref_put - decrement refcount for object.
83 * @release: pointer to the function that will clean up the object when the
84 * last reference to the object is released.
85 * This pointer is required, and it is not acceptable to pass kfree
86 * in as this function. If the caller does pass kfree to this
87 * function, you will be publicly mocked mercilessly by the kref
88 * maintainer, and anyone else who happens to notice it. You have
91 * Decrement the refcount, and if 0, call release().
92 * Return 1 if the object was removed, otherwise return 0. Beware, if this
93 * function returns 0, you still can not count on the kref from remaining in
94 * memory. Only use the return value if you want to see if the kref is now
97 static inline int kref_put(struct kref
*kref
, void (*release
)(struct kref
*kref
))
99 return kref_sub(kref
, 1, release
);
103 * kref_put_spinlock_irqsave - decrement refcount for object.
105 * @release: pointer to the function that will clean up the object when the
106 * last reference to the object is released.
107 * This pointer is required, and it is not acceptable to pass kfree
108 * in as this function.
109 * @lock: lock to take in release case
111 * Behaves identical to kref_put with one exception. If the reference count
112 * drops to zero, the lock will be taken atomically wrt dropping the reference
113 * count. The release function has to call spin_unlock() without _irqrestore.
115 static inline int kref_put_spinlock_irqsave(struct kref
*kref
,
116 void (*release
)(struct kref
*kref
),
121 WARN_ON(release
== NULL
);
122 if (atomic_add_unless(&kref
->refcount
, -1, 1))
124 spin_lock_irqsave(lock
, flags
);
125 if (atomic_dec_and_test(&kref
->refcount
)) {
127 local_irq_restore(flags
);
130 spin_unlock_irqrestore(lock
, flags
);
134 static inline int kref_put_mutex(struct kref
*kref
,
135 void (*release
)(struct kref
*kref
),
138 WARN_ON(release
== NULL
);
139 if (unlikely(!atomic_add_unless(&kref
->refcount
, -1, 1))) {
141 if (unlikely(!atomic_dec_and_test(&kref
->refcount
))) {
152 * kref_get_unless_zero - Increment refcount for object unless it is zero.
155 * Return non-zero if the increment succeeded. Otherwise return 0.
157 * This function is intended to simplify locking around refcounting for
158 * objects that can be looked up from a lookup structure, and which are
159 * removed from that lookup structure in the object destructor.
160 * Operations on such objects require at least a read lock around
161 * lookup + kref_get, and a write lock around kref_put + remove from lookup
162 * structure. Furthermore, RCU implementations become extremely tricky.
163 * With a lookup followed by a kref_get_unless_zero *with return value check*
164 * locking in the kref_put path can be deferred to the actual removal from
165 * the lookup structure and RCU lookups become trivial.
167 static inline int __must_check
kref_get_unless_zero(struct kref
*kref
)
169 return atomic_add_unless(&kref
->refcount
, 1, 0);
171 #endif /* _KREF_H_ */
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