include/linux/atomic.h

/* SPDX-License-Identifier: GPL-2.0 */
/* Atomic operations usable in machine independent code */
#ifndef _LINUX_ATOMIC_H
#define _LINUX_ATOMIC_H
#include <linux/types.h>

#include <asm/atomic.h>
#include <asm/barrier.h>

/*
 * Relaxed variants of xchg, cmpxchg and some atomic operations.
 *
 * We support four variants:
 *
 * - Fully ordered: The default implementation, no suffix required.
 * - Acquire: Provides ACQUIRE semantics, _acquire suffix.
 * - Release: Provides RELEASE semantics, _release suffix.
 * - Relaxed: No ordering guarantees, _relaxed suffix.
 *
 * For compound atomics performing both a load and a store, ACQUIRE
 * semantics apply only to the load and RELEASE semantics only to the
 * store portion of the operation. Note that a failed cmpxchg_acquire
 * does -not- imply any memory ordering constraints.
 *
 * See Documentation/memory-barriers.txt for ACQUIRE/RELEASE definitions.
 */

/*
 * The idea here is to build acquire/release variants by adding explicit
 * barriers on top of the relaxed variant. In the case where the relaxed
 * variant is already fully ordered, no additional barriers are needed.
 *
 * If an architecture overrides __atomic_acquire_fence() it will probably
 * want to define smp_mb__after_spinlock().
 */
#ifndef __atomic_acquire_fence
#define __atomic_acquire_fence		smp_mb__after_atomic
#endif

#ifndef __atomic_release_fence
#define __atomic_release_fence		smp_mb__before_atomic
#endif

#ifndef __atomic_pre_full_fence
#define __atomic_pre_full_fence		smp_mb__before_atomic
#endif

#ifndef __atomic_post_full_fence
#define __atomic_post_full_fence	smp_mb__after_atomic
#endif

#define __atomic_op_acquire(op, args...)				\
({									\
	typeof(op##_relaxed(args)) __ret  = op##_relaxed(args);		\
	__atomic_acquire_fence();					\
	__ret;								\
})

#define __atomic_op_release(op, args...)				\
({									\
	__atomic_release_fence();					\
	op##_relaxed(args);						\
})

#define __atomic_op_fence(op, args...)					\
({									\
	typeof(op##_relaxed(args)) __ret;				\
	__atomic_pre_full_fence();					\
	__ret = op##_relaxed(args);					\
	__atomic_post_full_fence();					\
	__ret;								\
})

#include <linux/atomic-fallback.h>

#include <asm-generic/atomic-long.h>

#endif /* _LINUX_ATOMIC_H */