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1// SPDX-License-Identifier: GPL-2.02#include <linux/export.h>3#include <linux/spinlock.h>4#include <linux/atomic.h>5 6/*7 * This is an implementation of the notion of "decrement a8 * reference count, and return locked if it decremented to zero".9 *10 * NOTE NOTE NOTE! This is _not_ equivalent to11 *12 * if (atomic_dec_and_test(&atomic)) {13 * spin_lock(&lock);14 * return 1;15 * }16 * return 0;17 *18 * because the spin-lock and the decrement must be19 * "atomic".20 */21int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)22{23 /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */24 if (atomic_add_unless(atomic, -1, 1))25 return 0;26 27 /* Otherwise do it the slow way */28 spin_lock(lock);29 if (atomic_dec_and_test(atomic))30 return 1;31 spin_unlock(lock);32 return 0;33}34 35EXPORT_SYMBOL(_atomic_dec_and_lock);36 37int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,38 unsigned long *flags)39{40 /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */41 if (atomic_add_unless(atomic, -1, 1))42 return 0;43 44 /* Otherwise do it the slow way */45 spin_lock_irqsave(lock, *flags);46 if (atomic_dec_and_test(atomic))47 return 1;48 spin_unlock_irqrestore(lock, *flags);49 return 0;50}51EXPORT_SYMBOL(_atomic_dec_and_lock_irqsave);52 53int _atomic_dec_and_raw_lock(atomic_t *atomic, raw_spinlock_t *lock)54{55 /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */56 if (atomic_add_unless(atomic, -1, 1))57 return 0;58 59 /* Otherwise do it the slow way */60 raw_spin_lock(lock);61 if (atomic_dec_and_test(atomic))62 return 1;63 raw_spin_unlock(lock);64 return 0;65}66EXPORT_SYMBOL(_atomic_dec_and_raw_lock);67 68int _atomic_dec_and_raw_lock_irqsave(atomic_t *atomic, raw_spinlock_t *lock,69 unsigned long *flags)70{71 /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */72 if (atomic_add_unless(atomic, -1, 1))73 return 0;74 75 /* Otherwise do it the slow way */76 raw_spin_lock_irqsave(lock, *flags);77 if (atomic_dec_and_test(atomic))78 return 1;79 raw_spin_unlock_irqrestore(lock, *flags);80 return 0;81}82EXPORT_SYMBOL(_atomic_dec_and_raw_lock_irqsave);83