| 1 | #include <linux/export.h> |
| 2 | #include <linux/lockref.h> |
| 3 | |
| 4 | #if USE_CMPXCHG_LOCKREF |
| 5 | |
| 6 | /* |
| 7 | * Allow weakly-ordered memory architectures to provide barrier-less |
| 8 | * cmpxchg semantics for lockref updates. |
| 9 | */ |
| 10 | #ifndef cmpxchg64_relaxed |
| 11 | # define cmpxchg64_relaxed cmpxchg64 |
| 12 | #endif |
| 13 | |
| 14 | /* |
| 15 | * Note that the "cmpxchg()" reloads the "old" value for the |
| 16 | * failure case. |
| 17 | */ |
| 18 | #define CMPXCHG_LOOP(CODE, SUCCESS) do { \ |
| 19 | struct lockref old; \ |
| 20 | BUILD_BUG_ON(sizeof(old) != 8); \ |
| 21 | old.lock_count = READ_ONCE(lockref->lock_count); \ |
| 22 | while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \ |
| 23 | struct lockref new = old, prev = old; \ |
| 24 | CODE \ |
| 25 | old.lock_count = cmpxchg64_relaxed(&lockref->lock_count, \ |
| 26 | old.lock_count, \ |
| 27 | new.lock_count); \ |
| 28 | if (likely(old.lock_count == prev.lock_count)) { \ |
| 29 | SUCCESS; \ |
| 30 | } \ |
| 31 | cpu_relax_lowlatency(); \ |
| 32 | } \ |
| 33 | } while (0) |
| 34 | |
| 35 | #else |
| 36 | |
| 37 | #define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0) |
| 38 | |
| 39 | #endif |
| 40 | |
| 41 | /** |
| 42 | * lockref_get - Increments reference count unconditionally |
| 43 | * @lockref: pointer to lockref structure |
| 44 | * |
| 45 | * This operation is only valid if you already hold a reference |
| 46 | * to the object, so you know the count cannot be zero. |
| 47 | */ |
| 48 | void lockref_get(struct lockref *lockref) |
| 49 | { |
| 50 | CMPXCHG_LOOP( |
| 51 | new.count++; |
| 52 | , |
| 53 | return; |
| 54 | ); |
| 55 | |
| 56 | spin_lock(&lockref->lock); |
| 57 | lockref->count++; |
| 58 | spin_unlock(&lockref->lock); |
| 59 | } |
| 60 | EXPORT_SYMBOL(lockref_get); |
| 61 | |
| 62 | /** |
| 63 | * lockref_get_not_zero - Increments count unless the count is 0 or dead |
| 64 | * @lockref: pointer to lockref structure |
| 65 | * Return: 1 if count updated successfully or 0 if count was zero |
| 66 | */ |
| 67 | int lockref_get_not_zero(struct lockref *lockref) |
| 68 | { |
| 69 | int retval; |
| 70 | |
| 71 | CMPXCHG_LOOP( |
| 72 | new.count++; |
| 73 | if (old.count <= 0) |
| 74 | return 0; |
| 75 | , |
| 76 | return 1; |
| 77 | ); |
| 78 | |
| 79 | spin_lock(&lockref->lock); |
| 80 | retval = 0; |
| 81 | if (lockref->count > 0) { |
| 82 | lockref->count++; |
| 83 | retval = 1; |
| 84 | } |
| 85 | spin_unlock(&lockref->lock); |
| 86 | return retval; |
| 87 | } |
| 88 | EXPORT_SYMBOL(lockref_get_not_zero); |
| 89 | |
| 90 | /** |
| 91 | * lockref_get_or_lock - Increments count unless the count is 0 or dead |
| 92 | * @lockref: pointer to lockref structure |
| 93 | * Return: 1 if count updated successfully or 0 if count was zero |
| 94 | * and we got the lock instead. |
| 95 | */ |
| 96 | int lockref_get_or_lock(struct lockref *lockref) |
| 97 | { |
| 98 | CMPXCHG_LOOP( |
| 99 | new.count++; |
| 100 | if (old.count <= 0) |
| 101 | break; |
| 102 | , |
| 103 | return 1; |
| 104 | ); |
| 105 | |
| 106 | spin_lock(&lockref->lock); |
| 107 | if (lockref->count <= 0) |
| 108 | return 0; |
| 109 | lockref->count++; |
| 110 | spin_unlock(&lockref->lock); |
| 111 | return 1; |
| 112 | } |
| 113 | EXPORT_SYMBOL(lockref_get_or_lock); |
| 114 | |
| 115 | /** |
| 116 | * lockref_put_return - Decrement reference count if possible |
| 117 | * @lockref: pointer to lockref structure |
| 118 | * |
| 119 | * Decrement the reference count and return the new value. |
| 120 | * If the lockref was dead or locked, return an error. |
| 121 | */ |
| 122 | int lockref_put_return(struct lockref *lockref) |
| 123 | { |
| 124 | CMPXCHG_LOOP( |
| 125 | new.count--; |
| 126 | if (old.count <= 0) |
| 127 | return -1; |
| 128 | , |
| 129 | return new.count; |
| 130 | ); |
| 131 | return -1; |
| 132 | } |
| 133 | EXPORT_SYMBOL(lockref_put_return); |
| 134 | |
| 135 | /** |
| 136 | * lockref_put_or_lock - decrements count unless count <= 1 before decrement |
| 137 | * @lockref: pointer to lockref structure |
| 138 | * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken |
| 139 | */ |
| 140 | int lockref_put_or_lock(struct lockref *lockref) |
| 141 | { |
| 142 | CMPXCHG_LOOP( |
| 143 | new.count--; |
| 144 | if (old.count <= 1) |
| 145 | break; |
| 146 | , |
| 147 | return 1; |
| 148 | ); |
| 149 | |
| 150 | spin_lock(&lockref->lock); |
| 151 | if (lockref->count <= 1) |
| 152 | return 0; |
| 153 | lockref->count--; |
| 154 | spin_unlock(&lockref->lock); |
| 155 | return 1; |
| 156 | } |
| 157 | EXPORT_SYMBOL(lockref_put_or_lock); |
| 158 | |
| 159 | /** |
| 160 | * lockref_mark_dead - mark lockref dead |
| 161 | * @lockref: pointer to lockref structure |
| 162 | */ |
| 163 | void lockref_mark_dead(struct lockref *lockref) |
| 164 | { |
| 165 | assert_spin_locked(&lockref->lock); |
| 166 | lockref->count = -128; |
| 167 | } |
| 168 | EXPORT_SYMBOL(lockref_mark_dead); |
| 169 | |
| 170 | /** |
| 171 | * lockref_get_not_dead - Increments count unless the ref is dead |
| 172 | * @lockref: pointer to lockref structure |
| 173 | * Return: 1 if count updated successfully or 0 if lockref was dead |
| 174 | */ |
| 175 | int lockref_get_not_dead(struct lockref *lockref) |
| 176 | { |
| 177 | int retval; |
| 178 | |
| 179 | CMPXCHG_LOOP( |
| 180 | new.count++; |
| 181 | if (old.count < 0) |
| 182 | return 0; |
| 183 | , |
| 184 | return 1; |
| 185 | ); |
| 186 | |
| 187 | spin_lock(&lockref->lock); |
| 188 | retval = 0; |
| 189 | if (lockref->count >= 0) { |
| 190 | lockref->count++; |
| 191 | retval = 1; |
| 192 | } |
| 193 | spin_unlock(&lockref->lock); |
| 194 | return retval; |
| 195 | } |
| 196 | EXPORT_SYMBOL(lockref_get_not_dead); |