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lib/lockref.c
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#include <linux/export.h> #include <linux/lockref.h> |
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#if USE_CMPXCHG_LOCKREF |
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/* |
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* Allow weakly-ordered memory architectures to provide barrier-less * cmpxchg semantics for lockref updates. */ #ifndef cmpxchg64_relaxed # define cmpxchg64_relaxed cmpxchg64 #endif /* |
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* Note that the "cmpxchg()" reloads the "old" value for the * failure case. */ #define CMPXCHG_LOOP(CODE, SUCCESS) do { \ struct lockref old; \ BUILD_BUG_ON(sizeof(old) != 8); \ old.lock_count = ACCESS_ONCE(lockref->lock_count); \ while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \ struct lockref new = old, prev = old; \ CODE \ |
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old.lock_count = cmpxchg64_relaxed(&lockref->lock_count, \ old.lock_count, \ new.lock_count); \ |
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if (likely(old.lock_count == prev.lock_count)) { \ SUCCESS; \ } \ |
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cpu_relax_lowlatency(); \ |
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} \ } while (0) #else #define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0) #endif |
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/** * lockref_get - Increments reference count unconditionally |
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* @lockref: pointer to lockref structure |
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* * This operation is only valid if you already hold a reference * to the object, so you know the count cannot be zero. */ void lockref_get(struct lockref *lockref) { |
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CMPXCHG_LOOP( new.count++; , return; ); |
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spin_lock(&lockref->lock); lockref->count++; spin_unlock(&lockref->lock); } EXPORT_SYMBOL(lockref_get); /** * lockref_get_not_zero - Increments count unless the count is 0 |
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* @lockref: pointer to lockref structure |
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* Return: 1 if count updated successfully or 0 if count was zero */ int lockref_get_not_zero(struct lockref *lockref) { |
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int retval; CMPXCHG_LOOP( new.count++; if (!old.count) return 0; , return 1; ); |
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spin_lock(&lockref->lock); |
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retval = 0; |
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if (lockref->count) { lockref->count++; retval = 1; } spin_unlock(&lockref->lock); return retval; } EXPORT_SYMBOL(lockref_get_not_zero); /** * lockref_get_or_lock - Increments count unless the count is 0 |
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* @lockref: pointer to lockref structure |
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* Return: 1 if count updated successfully or 0 if count was zero * and we got the lock instead. */ int lockref_get_or_lock(struct lockref *lockref) { |
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CMPXCHG_LOOP( new.count++; if (!old.count) break; , return 1; ); |
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spin_lock(&lockref->lock); if (!lockref->count) return 0; lockref->count++; spin_unlock(&lockref->lock); return 1; } EXPORT_SYMBOL(lockref_get_or_lock); /** * lockref_put_or_lock - decrements count unless count <= 1 before decrement |
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* @lockref: pointer to lockref structure |
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* Return: 1 if count updated successfully or 0 if count <= 1 and lock taken */ int lockref_put_or_lock(struct lockref *lockref) { |
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CMPXCHG_LOOP( new.count--; if (old.count <= 1) break; , return 1; ); |
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spin_lock(&lockref->lock); if (lockref->count <= 1) return 0; lockref->count--; spin_unlock(&lockref->lock); return 1; } EXPORT_SYMBOL(lockref_put_or_lock); |
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/** * lockref_mark_dead - mark lockref dead * @lockref: pointer to lockref structure */ void lockref_mark_dead(struct lockref *lockref) { assert_spin_locked(&lockref->lock); lockref->count = -128; } |
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EXPORT_SYMBOL(lockref_mark_dead); |
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/** * lockref_get_not_dead - Increments count unless the ref is dead * @lockref: pointer to lockref structure * Return: 1 if count updated successfully or 0 if lockref was dead */ int lockref_get_not_dead(struct lockref *lockref) { int retval; CMPXCHG_LOOP( new.count++; if ((int)old.count < 0) return 0; , return 1; ); spin_lock(&lockref->lock); retval = 0; if ((int) lockref->count >= 0) { lockref->count++; retval = 1; } spin_unlock(&lockref->lock); return retval; } EXPORT_SYMBOL(lockref_get_not_dead); |