Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | /* |
Robert P. J. Day | 932fb06 | 2010-03-13 07:58:13 -0500 | [diff] [blame] | 2 | * kref.h - library routines for handling generic reference counted objects |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 | |
Greg Kroah-Hartman | 6261dde | 2011-12-14 11:19:07 -0800 | [diff] [blame] | 18 | #include <linux/bug.h> |
| 19 | #include <linux/atomic.h> |
James Bottomley | 67175b8 | 2012-01-17 21:14:05 +0000 | [diff] [blame] | 20 | #include <linux/kernel.h> |
Al Viro | 8ad5db8 | 2012-08-17 20:10:46 -0400 | [diff] [blame] | 21 | #include <linux/mutex.h> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 22 | |
| 23 | struct kref { |
| 24 | atomic_t refcount; |
| 25 | }; |
| 26 | |
Peter Zijlstra | 4af679c | 2011-12-13 10:36:20 +0100 | [diff] [blame] | 27 | /** |
| 28 | * kref_init - initialize object. |
| 29 | * @kref: object in question. |
| 30 | */ |
| 31 | static inline void kref_init(struct kref *kref) |
| 32 | { |
| 33 | atomic_set(&kref->refcount, 1); |
Peter Zijlstra | 4af679c | 2011-12-13 10:36:20 +0100 | [diff] [blame] | 34 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 35 | |
Peter Zijlstra | ea9df3c | 2016-11-14 17:29:48 +0100 | [diff] [blame] | 36 | static inline int kref_read(const struct kref *kref) |
| 37 | { |
| 38 | return atomic_read(&kref->refcount); |
| 39 | } |
| 40 | |
Peter Zijlstra | 4af679c | 2011-12-13 10:36:20 +0100 | [diff] [blame] | 41 | /** |
| 42 | * kref_get - increment refcount for object. |
| 43 | * @kref: object. |
| 44 | */ |
| 45 | static inline void kref_get(struct kref *kref) |
| 46 | { |
Anatol Pomozov | 2d864e4 | 2013-05-07 15:37:48 -0700 | [diff] [blame] | 47 | /* If refcount was 0 before incrementing then we have a race |
| 48 | * condition when this kref is freeing by some other thread right now. |
| 49 | * In this case one should use kref_get_unless_zero() |
| 50 | */ |
| 51 | WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2); |
Peter Zijlstra | 4af679c | 2011-12-13 10:36:20 +0100 | [diff] [blame] | 52 | } |
| 53 | |
| 54 | /** |
Peter Zijlstra | 4af679c | 2011-12-13 10:36:20 +0100 | [diff] [blame] | 55 | * kref_sub - subtract a number of refcounts for object. |
| 56 | * @kref: object. |
| 57 | * @count: Number of recounts to subtract. |
| 58 | * @release: pointer to the function that will clean up the object when the |
| 59 | * last reference to the object is released. |
| 60 | * This pointer is required, and it is not acceptable to pass kfree |
Greg Kroah-Hartman | 6261dde | 2011-12-14 11:19:07 -0800 | [diff] [blame] | 61 | * in as this function. If the caller does pass kfree to this |
| 62 | * function, you will be publicly mocked mercilessly by the kref |
| 63 | * maintainer, and anyone else who happens to notice it. You have |
| 64 | * been warned. |
Peter Zijlstra | 4af679c | 2011-12-13 10:36:20 +0100 | [diff] [blame] | 65 | * |
| 66 | * Subtract @count from the refcount, and if 0, call release(). |
| 67 | * Return 1 if the object was removed, otherwise return 0. Beware, if this |
| 68 | * function returns 0, you still can not count on the kref from remaining in |
| 69 | * memory. Only use the return value if you want to see if the kref is now |
| 70 | * gone, not present. |
| 71 | */ |
| 72 | static inline int kref_sub(struct kref *kref, unsigned int count, |
| 73 | void (*release)(struct kref *kref)) |
| 74 | { |
| 75 | WARN_ON(release == NULL); |
Peter Zijlstra | 4af679c | 2011-12-13 10:36:20 +0100 | [diff] [blame] | 76 | |
| 77 | if (atomic_sub_and_test((int) count, &kref->refcount)) { |
| 78 | release(kref); |
| 79 | return 1; |
| 80 | } |
| 81 | return 0; |
| 82 | } |
Peter Zijlstra | 47dbd7d | 2011-12-10 11:43:43 +0100 | [diff] [blame] | 83 | |
| 84 | /** |
| 85 | * kref_put - decrement refcount for object. |
| 86 | * @kref: object. |
| 87 | * @release: pointer to the function that will clean up the object when the |
| 88 | * last reference to the object is released. |
| 89 | * This pointer is required, and it is not acceptable to pass kfree |
Greg Kroah-Hartman | 6261dde | 2011-12-14 11:19:07 -0800 | [diff] [blame] | 90 | * in as this function. If the caller does pass kfree to this |
| 91 | * function, you will be publicly mocked mercilessly by the kref |
| 92 | * maintainer, and anyone else who happens to notice it. You have |
| 93 | * been warned. |
Peter Zijlstra | 47dbd7d | 2011-12-10 11:43:43 +0100 | [diff] [blame] | 94 | * |
| 95 | * Decrement the refcount, and if 0, call release(). |
| 96 | * Return 1 if the object was removed, otherwise return 0. Beware, if this |
| 97 | * function returns 0, you still can not count on the kref from remaining in |
| 98 | * memory. Only use the return value if you want to see if the kref is now |
| 99 | * gone, not present. |
| 100 | */ |
| 101 | static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) |
| 102 | { |
| 103 | return kref_sub(kref, 1, release); |
| 104 | } |
Al Viro | 8ad5db8 | 2012-08-17 20:10:46 -0400 | [diff] [blame] | 105 | |
| 106 | static inline int kref_put_mutex(struct kref *kref, |
| 107 | void (*release)(struct kref *kref), |
| 108 | struct mutex *lock) |
| 109 | { |
| 110 | WARN_ON(release == NULL); |
Anatol Pomozov | 2d864e4 | 2013-05-07 15:37:48 -0700 | [diff] [blame] | 111 | if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) { |
Al Viro | 8ad5db8 | 2012-08-17 20:10:46 -0400 | [diff] [blame] | 112 | mutex_lock(lock); |
| 113 | if (unlikely(!atomic_dec_and_test(&kref->refcount))) { |
| 114 | mutex_unlock(lock); |
| 115 | return 0; |
| 116 | } |
| 117 | release(kref); |
| 118 | return 1; |
| 119 | } |
| 120 | return 0; |
| 121 | } |
Thomas Hellstrom | 4b20db3 | 2012-11-06 11:31:49 +0000 | [diff] [blame] | 122 | |
| 123 | /** |
| 124 | * kref_get_unless_zero - Increment refcount for object unless it is zero. |
| 125 | * @kref: object. |
| 126 | * |
| 127 | * Return non-zero if the increment succeeded. Otherwise return 0. |
| 128 | * |
| 129 | * This function is intended to simplify locking around refcounting for |
| 130 | * objects that can be looked up from a lookup structure, and which are |
| 131 | * removed from that lookup structure in the object destructor. |
| 132 | * Operations on such objects require at least a read lock around |
| 133 | * lookup + kref_get, and a write lock around kref_put + remove from lookup |
| 134 | * structure. Furthermore, RCU implementations become extremely tricky. |
| 135 | * With a lookup followed by a kref_get_unless_zero *with return value check* |
| 136 | * locking in the kref_put path can be deferred to the actual removal from |
| 137 | * the lookup structure and RCU lookups become trivial. |
| 138 | */ |
| 139 | static inline int __must_check kref_get_unless_zero(struct kref *kref) |
| 140 | { |
| 141 | return atomic_add_unless(&kref->refcount, 1, 0); |
| 142 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 143 | #endif /* _KREF_H_ */ |