Linus Torvalds | 2f4f12e | 2013-09-02 11:58:20 -0700 | [diff] [blame] | 1 | #include <linux/export.h> |
| 2 | #include <linux/lockref.h> |
| 3 | |
Linus Torvalds | bc08b44 | 2013-09-02 12:12:15 -0700 | [diff] [blame] | 4 | #ifdef CONFIG_CMPXCHG_LOCKREF |
| 5 | |
| 6 | /* |
| 7 | * Note that the "cmpxchg()" reloads the "old" value for the |
| 8 | * failure case. |
| 9 | */ |
| 10 | #define CMPXCHG_LOOP(CODE, SUCCESS) do { \ |
| 11 | struct lockref old; \ |
| 12 | BUILD_BUG_ON(sizeof(old) != 8); \ |
| 13 | old.lock_count = ACCESS_ONCE(lockref->lock_count); \ |
| 14 | while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \ |
| 15 | struct lockref new = old, prev = old; \ |
| 16 | CODE \ |
| 17 | old.lock_count = cmpxchg(&lockref->lock_count, \ |
| 18 | old.lock_count, new.lock_count); \ |
| 19 | if (likely(old.lock_count == prev.lock_count)) { \ |
| 20 | SUCCESS; \ |
| 21 | } \ |
Luck, Tony | d472d9d | 2013-09-03 14:49:49 -0700 | [diff] [blame^] | 22 | cpu_relax(); \ |
Linus Torvalds | bc08b44 | 2013-09-02 12:12:15 -0700 | [diff] [blame] | 23 | } \ |
| 24 | } while (0) |
| 25 | |
| 26 | #else |
| 27 | |
| 28 | #define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0) |
| 29 | |
| 30 | #endif |
| 31 | |
Linus Torvalds | 2f4f12e | 2013-09-02 11:58:20 -0700 | [diff] [blame] | 32 | /** |
| 33 | * lockref_get - Increments reference count unconditionally |
| 34 | * @lockcnt: pointer to lockref structure |
| 35 | * |
| 36 | * This operation is only valid if you already hold a reference |
| 37 | * to the object, so you know the count cannot be zero. |
| 38 | */ |
| 39 | void lockref_get(struct lockref *lockref) |
| 40 | { |
Linus Torvalds | bc08b44 | 2013-09-02 12:12:15 -0700 | [diff] [blame] | 41 | CMPXCHG_LOOP( |
| 42 | new.count++; |
| 43 | , |
| 44 | return; |
| 45 | ); |
| 46 | |
Linus Torvalds | 2f4f12e | 2013-09-02 11:58:20 -0700 | [diff] [blame] | 47 | spin_lock(&lockref->lock); |
| 48 | lockref->count++; |
| 49 | spin_unlock(&lockref->lock); |
| 50 | } |
| 51 | EXPORT_SYMBOL(lockref_get); |
| 52 | |
| 53 | /** |
| 54 | * lockref_get_not_zero - Increments count unless the count is 0 |
| 55 | * @lockcnt: pointer to lockref structure |
| 56 | * Return: 1 if count updated successfully or 0 if count was zero |
| 57 | */ |
| 58 | int lockref_get_not_zero(struct lockref *lockref) |
| 59 | { |
Linus Torvalds | bc08b44 | 2013-09-02 12:12:15 -0700 | [diff] [blame] | 60 | int retval; |
| 61 | |
| 62 | CMPXCHG_LOOP( |
| 63 | new.count++; |
| 64 | if (!old.count) |
| 65 | return 0; |
| 66 | , |
| 67 | return 1; |
| 68 | ); |
Linus Torvalds | 2f4f12e | 2013-09-02 11:58:20 -0700 | [diff] [blame] | 69 | |
| 70 | spin_lock(&lockref->lock); |
Linus Torvalds | bc08b44 | 2013-09-02 12:12:15 -0700 | [diff] [blame] | 71 | retval = 0; |
Linus Torvalds | 2f4f12e | 2013-09-02 11:58:20 -0700 | [diff] [blame] | 72 | if (lockref->count) { |
| 73 | lockref->count++; |
| 74 | retval = 1; |
| 75 | } |
| 76 | spin_unlock(&lockref->lock); |
| 77 | return retval; |
| 78 | } |
| 79 | EXPORT_SYMBOL(lockref_get_not_zero); |
| 80 | |
| 81 | /** |
| 82 | * lockref_get_or_lock - Increments count unless the count is 0 |
| 83 | * @lockcnt: pointer to lockref structure |
| 84 | * Return: 1 if count updated successfully or 0 if count was zero |
| 85 | * and we got the lock instead. |
| 86 | */ |
| 87 | int lockref_get_or_lock(struct lockref *lockref) |
| 88 | { |
Linus Torvalds | bc08b44 | 2013-09-02 12:12:15 -0700 | [diff] [blame] | 89 | CMPXCHG_LOOP( |
| 90 | new.count++; |
| 91 | if (!old.count) |
| 92 | break; |
| 93 | , |
| 94 | return 1; |
| 95 | ); |
| 96 | |
Linus Torvalds | 2f4f12e | 2013-09-02 11:58:20 -0700 | [diff] [blame] | 97 | spin_lock(&lockref->lock); |
| 98 | if (!lockref->count) |
| 99 | return 0; |
| 100 | lockref->count++; |
| 101 | spin_unlock(&lockref->lock); |
| 102 | return 1; |
| 103 | } |
| 104 | EXPORT_SYMBOL(lockref_get_or_lock); |
| 105 | |
| 106 | /** |
| 107 | * lockref_put_or_lock - decrements count unless count <= 1 before decrement |
| 108 | * @lockcnt: pointer to lockref structure |
| 109 | * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken |
| 110 | */ |
| 111 | int lockref_put_or_lock(struct lockref *lockref) |
| 112 | { |
Linus Torvalds | bc08b44 | 2013-09-02 12:12:15 -0700 | [diff] [blame] | 113 | CMPXCHG_LOOP( |
| 114 | new.count--; |
| 115 | if (old.count <= 1) |
| 116 | break; |
| 117 | , |
| 118 | return 1; |
| 119 | ); |
| 120 | |
Linus Torvalds | 2f4f12e | 2013-09-02 11:58:20 -0700 | [diff] [blame] | 121 | spin_lock(&lockref->lock); |
| 122 | if (lockref->count <= 1) |
| 123 | return 0; |
| 124 | lockref->count--; |
| 125 | spin_unlock(&lockref->lock); |
| 126 | return 1; |
| 127 | } |
| 128 | EXPORT_SYMBOL(lockref_put_or_lock); |