cregit-Linux how code gets into the kernel

Release 4.13 lib/lockref.c

Directory: lib
#include <linux/export.h>
#include <linux/lockref.h>

#if USE_CMPXCHG_LOCKREF

/*
 * 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 = READ_ONCE(lockref->lock_count);                        \
        while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) {     \
                struct lockref new = old, prev = old;                           \
                CODE                                                            \
                old.lock_count = cmpxchg64_relaxed(&lockref->lock_count,        \
                                                   old.lock_count,              \
                                                   new.lock_count);             \
                if (likely(old.lock_count == prev.lock_count)) {                \
                        SUCCESS;                                                \
                }                                                               \
                cpu_relax();                                                    \
        }                                                                       \
} while (0)

#else


#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)

#endif

/**
 * lockref_get - Increments reference count unconditionally
 * @lockref: pointer to lockref structure
 *
 * 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) { CMPXCHG_LOOP( new.count++; , return; ); spin_lock(&lockref->lock); lockref->count++; spin_unlock(&lockref->lock); }

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Linus Torvalds38100.00%2100.00%
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EXPORT_SYMBOL(lockref_get); /** * lockref_get_not_zero - Increments count unless the count is 0 or dead * @lockref: pointer to lockref structure * Return: 1 if count updated successfully or 0 if count was zero */
int lockref_get_not_zero(struct lockref *lockref) { int retval; CMPXCHG_LOOP( new.count++; if (old.count <= 0) return 0; , return 1; ); spin_lock(&lockref->lock); retval = 0; if (lockref->count > 0) { lockref->count++; retval = 1; } spin_unlock(&lockref->lock); return retval; }

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Linus Torvalds68100.00%3100.00%
Total68100.00%3100.00%

EXPORT_SYMBOL(lockref_get_not_zero); /** * lockref_get_or_lock - Increments count unless the count is 0 or dead * @lockref: pointer to lockref structure * 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) { CMPXCHG_LOOP( new.count++; if (old.count <= 0) break; , return 1; ); spin_lock(&lockref->lock); if (lockref->count <= 0) return 0; lockref->count++; spin_unlock(&lockref->lock); return 1; }

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Linus Torvalds56100.00%3100.00%
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EXPORT_SYMBOL(lockref_get_or_lock); /** * lockref_put_return - Decrement reference count if possible * @lockref: pointer to lockref structure * * Decrement the reference count and return the new value. * If the lockref was dead or locked, return an error. */
int lockref_put_return(struct lockref *lockref) { CMPXCHG_LOOP( new.count--; if (old.count <= 0) return -1; , return new.count; ); return -1; }

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Linus Torvalds25100.00%1100.00%
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EXPORT_SYMBOL(lockref_put_return); /** * lockref_put_or_lock - decrements count unless count <= 1 before decrement * @lockref: pointer to lockref structure * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken */
int lockref_put_or_lock(struct lockref *lockref) { CMPXCHG_LOOP( new.count--; if (old.count <= 1) break; , return 1; ); spin_lock(&lockref->lock); if (lockref->count <= 1) return 0; lockref->count--; spin_unlock(&lockref->lock); return 1; }

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Linus Torvalds56100.00%2100.00%
Total56100.00%2100.00%

EXPORT_SYMBOL(lockref_put_or_lock); /** * 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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Linus Torvalds25100.00%1100.00%
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EXPORT_SYMBOL(lockref_mark_dead); /** * 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 (old.count < 0) return 0; , return 1; ); spin_lock(&lockref->lock); retval = 0; if (lockref->count >= 0) { lockref->count++; retval = 1; } spin_unlock(&lockref->lock); return retval; }

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Linus Torvalds68100.00%2100.00%
Total68100.00%2100.00%

EXPORT_SYMBOL(lockref_get_not_dead);

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Linus Torvalds40197.80%562.50%
Steven Whitehouse51.22%112.50%
Peter Zijlstra30.73%112.50%
Christian Bornträger10.24%112.50%
Total410100.00%8100.00%
Directory: lib
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