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1 | /* |
2 | * kref.h - library routines for handling generic reference counted objects |
3 | * |
4 | * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com> |
5 | * Copyright (C) 2004 IBM Corp. |
6 | * |
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 |
10 | * |
11 | * This file is released under the GPLv2. |
12 | * |
13 | */ |
14 | |
15 | #ifndef _KREF_H_ |
16 | #define _KREF_H_ |
17 | |
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> |
23 | |
24 | struct kref { |
25 | atomic_t refcount; |
26 | }; |
27 | |
28 | /** |
29 | * kref_init - initialize object. |
30 | * @kref: object in question. |
31 | */ |
32 | static inline void kref_init(struct kref *kref) |
33 | { |
34 | atomic_set(&kref->refcount, 1); |
35 | } |
36 | |
37 | /** |
38 | * kref_get - increment refcount for object. |
39 | * @kref: object. |
40 | */ |
41 | static inline void kref_get(struct kref *kref) |
42 | { |
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() |
46 | */ |
47 | WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2); |
48 | } |
49 | |
50 | /** |
51 | * kref_sub - subtract a number of refcounts for object. |
52 | * @kref: 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 |
60 | * been warned. |
61 | * |
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 |
66 | * gone, not present. |
67 | */ |
68 | static inline int kref_sub(struct kref *kref, unsigned int count, |
69 | void (*release)(struct kref *kref)) |
70 | { |
71 | WARN_ON(release == NULL); |
72 | |
73 | if (atomic_sub_and_test((int) count, &kref->refcount)) { |
74 | release(kref); |
75 | return 1; |
76 | } |
77 | return 0; |
78 | } |
79 | |
80 | /** |
81 | * kref_put - decrement refcount for object. |
82 | * @kref: 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 |
89 | * been warned. |
90 | * |
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 |
95 | * gone, not present. |
96 | */ |
97 | static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) |
98 | { |
99 | return kref_sub(kref, 1, release); |
100 | } |
101 | |
102 | /** |
103 | * kref_put_spinlock_irqsave - decrement refcount for object. |
104 | * @kref: 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 |
110 | * |
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. |
114 | */ |
115 | static inline int kref_put_spinlock_irqsave(struct kref *kref, |
116 | void (*release)(struct kref *kref), |
117 | spinlock_t *lock) |
118 | { |
119 | unsigned long flags; |
120 | |
121 | WARN_ON(release == NULL); |
122 | if (atomic_add_unless(&kref->refcount, -1, 1)) |
123 | return 0; |
124 | spin_lock_irqsave(lock, flags); |
125 | if (atomic_dec_and_test(&kref->refcount)) { |
126 | release(kref); |
127 | local_irq_restore(flags); |
128 | return 1; |
129 | } |
130 | spin_unlock_irqrestore(lock, flags); |
131 | return 0; |
132 | } |
133 | |
134 | static inline int kref_put_mutex(struct kref *kref, |
135 | void (*release)(struct kref *kref), |
136 | struct mutex *lock) |
137 | { |
138 | WARN_ON(release == NULL); |
139 | if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) { |
140 | mutex_lock(lock); |
141 | if (unlikely(!atomic_dec_and_test(&kref->refcount))) { |
142 | mutex_unlock(lock); |
143 | return 0; |
144 | } |
145 | release(kref); |
146 | return 1; |
147 | } |
148 | return 0; |
149 | } |
150 | |
151 | /** |
152 | * kref_get_unless_zero - Increment refcount for object unless it is zero. |
153 | * @kref: object. |
154 | * |
155 | * Return non-zero if the increment succeeded. Otherwise return 0. |
156 | * |
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. |
166 | */ |
167 | static inline int __must_check kref_get_unless_zero(struct kref *kref) |
168 | { |
169 | return atomic_add_unless(&kref->refcount, 1, 0); |
170 | } |
171 | #endif /* _KREF_H_ */ |
172 |
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