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| Rev | Author | Line No. | Line |
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| 1408 | serge | 1 | /* |
| 1964 | serge | 2 | * kref.h - library routines for handling generic reference counted objects |
| 1408 | serge | 3 | * |
| 4 | * Copyright (C) 2004 Greg Kroah-Hartman |
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| 5 | * Copyright (C) 2004 IBM Corp. |
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| 6 | * |
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| 7 | * based on kobject.h which was: |
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| 8 | * Copyright (C) 2002-2003 Patrick Mochel |
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| 9 | * Copyright (C) 2002-2003 Open Source Development Labs |
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| 10 | * |
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| 11 | * This file is released under the GPLv2. |
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| 12 | * |
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| 13 | */ |
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| 14 | |||
| 15 | #ifndef _KREF_H_ |
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| 16 | #define _KREF_H_ |
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| 17 | |||
| 5270 | serge | 18 | #include |
| 19 | #include |
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| 20 | #include |
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| 21 | #include |
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| 22 | #include |
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| 1408 | serge | 23 | |
| 24 | struct kref { |
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| 25 | atomic_t refcount; |
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| 26 | }; |
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| 27 | |||
| 6082 | serge | 28 | /** |
| 29 | * kref_init - initialize object. |
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| 30 | * @kref: object in question. |
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| 31 | */ |
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| 32 | static inline void kref_init(struct kref *kref) |
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| 33 | { |
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| 34 | atomic_set(&kref->refcount, 1); |
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| 35 | } |
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| 1408 | serge | 36 | |
| 6082 | serge | 37 | /** |
| 38 | * kref_get - increment refcount for object. |
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| 39 | * @kref: object. |
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| 40 | */ |
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| 41 | static inline void kref_get(struct kref *kref) |
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| 42 | { |
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| 43 | /* If refcount was 0 before incrementing then we have a race |
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| 44 | * condition when this kref is freeing by some other thread right now. |
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| 45 | * In this case one should use kref_get_unless_zero() |
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| 46 | */ |
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| 47 | WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2); |
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| 48 | } |
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| 49 | |||
| 50 | /** |
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| 51 | * kref_sub - subtract a number of refcounts for object. |
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| 52 | * @kref: object. |
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| 53 | * @count: Number of recounts to subtract. |
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| 54 | * @release: pointer to the function that will clean up the object when the |
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| 55 | * last reference to the object is released. |
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| 56 | * This pointer is required, and it is not acceptable to pass kfree |
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| 57 | * in as this function. If the caller does pass kfree to this |
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| 58 | * function, you will be publicly mocked mercilessly by the kref |
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| 59 | * maintainer, and anyone else who happens to notice it. You have |
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| 60 | * been warned. |
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| 61 | * |
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| 62 | * Subtract @count from the refcount, and if 0, call release(). |
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| 63 | * Return 1 if the object was removed, otherwise return 0. Beware, if this |
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| 64 | * function returns 0, you still can not count on the kref from remaining in |
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| 65 | * memory. Only use the return value if you want to see if the kref is now |
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| 66 | * gone, not present. |
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| 67 | */ |
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| 68 | static inline int kref_sub(struct kref *kref, unsigned int count, |
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| 69 | void (*release)(struct kref *kref)) |
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| 70 | { |
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| 71 | WARN_ON(release == NULL); |
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| 72 | |||
| 73 | if (atomic_sub_and_test((int) count, &kref->refcount)) { |
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| 74 | release(kref); |
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| 75 | return 1; |
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| 76 | } |
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| 77 | return 0; |
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| 78 | } |
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| 79 | |||
| 80 | /** |
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| 81 | * kref_put - decrement refcount for object. |
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| 82 | * @kref: object. |
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| 83 | * @release: pointer to the function that will clean up the object when the |
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| 84 | * last reference to the object is released. |
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| 85 | * This pointer is required, and it is not acceptable to pass kfree |
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| 86 | * in as this function. If the caller does pass kfree to this |
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| 87 | * function, you will be publicly mocked mercilessly by the kref |
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| 88 | * maintainer, and anyone else who happens to notice it. You have |
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| 89 | * been warned. |
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| 90 | * |
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| 91 | * Decrement the refcount, and if 0, call release(). |
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| 92 | * Return 1 if the object was removed, otherwise return 0. Beware, if this |
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| 93 | * function returns 0, you still can not count on the kref from remaining in |
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| 94 | * memory. Only use the return value if you want to see if the kref is now |
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| 95 | * gone, not present. |
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| 96 | */ |
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| 97 | static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) |
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| 98 | { |
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| 99 | return kref_sub(kref, 1, release); |
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| 100 | } |
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| 101 | |||
| 102 | /** |
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| 103 | * kref_put_spinlock_irqsave - decrement refcount for object. |
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| 104 | * @kref: object. |
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| 105 | * @release: pointer to the function that will clean up the object when the |
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| 106 | * last reference to the object is released. |
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| 107 | * This pointer is required, and it is not acceptable to pass kfree |
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| 108 | * in as this function. |
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| 109 | * @lock: lock to take in release case |
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| 110 | * |
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| 111 | * Behaves identical to kref_put with one exception. If the reference count |
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| 112 | * drops to zero, the lock will be taken atomically wrt dropping the reference |
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| 113 | * count. The release function has to call spin_unlock() without _irqrestore. |
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| 114 | */ |
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| 115 | static inline int kref_put_spinlock_irqsave(struct kref *kref, |
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| 116 | void (*release)(struct kref *kref), |
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| 117 | spinlock_t *lock) |
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| 118 | { |
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| 119 | unsigned long flags; |
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| 120 | |||
| 121 | WARN_ON(release == NULL); |
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| 122 | if (atomic_add_unless(&kref->refcount, -1, 1)) |
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| 123 | return 0; |
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| 124 | spin_lock_irqsave(lock, flags); |
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| 125 | if (atomic_dec_and_test(&kref->refcount)) { |
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| 126 | release(kref); |
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| 127 | local_irq_restore(flags); |
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| 128 | return 1; |
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| 129 | } |
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| 130 | spin_unlock_irqrestore(lock, flags); |
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| 131 | return 0; |
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| 132 | } |
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| 133 | |||
| 134 | static inline int kref_put_mutex(struct kref *kref, |
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| 135 | void (*release)(struct kref *kref), |
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| 136 | struct mutex *lock) |
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| 137 | { |
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| 138 | WARN_ON(release == NULL); |
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| 139 | if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) { |
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| 140 | mutex_lock(lock); |
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| 141 | if (unlikely(!atomic_dec_and_test(&kref->refcount))) { |
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| 142 | mutex_unlock(lock); |
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| 143 | return 0; |
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| 144 | } |
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| 145 | release(kref); |
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| 146 | return 1; |
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| 147 | } |
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| 148 | return 0; |
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| 149 | } |
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| 150 | |||
| 151 | /** |
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| 152 | * kref_get_unless_zero - Increment refcount for object unless it is zero. |
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| 153 | * @kref: object. |
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| 154 | * |
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| 155 | * Return non-zero if the increment succeeded. Otherwise return 0. |
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| 156 | * |
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| 157 | * This function is intended to simplify locking around refcounting for |
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| 158 | * objects that can be looked up from a lookup structure, and which are |
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| 159 | * removed from that lookup structure in the object destructor. |
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| 160 | * Operations on such objects require at least a read lock around |
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| 161 | * lookup + kref_get, and a write lock around kref_put + remove from lookup |
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| 162 | * structure. Furthermore, RCU implementations become extremely tricky. |
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| 163 | * With a lookup followed by a kref_get_unless_zero *with return value check* |
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| 164 | * locking in the kref_put path can be deferred to the actual removal from |
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| 165 | * the lookup structure and RCU lookups become trivial. |
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| 166 | */ |
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| 167 | static inline int __must_check kref_get_unless_zero(struct kref *kref) |
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| 168 | { |
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| 169 | return atomic_add_unless(&kref->refcount, 1, 0); |
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| 170 | } |
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| 1408 | serge | 171 | #endif /* _KREF_H_ */ |