locking/atomic/x86: Introduce arch_atomic64_read_nonatomic() to x86_32

#define ATOMIC64_INIT(val)	{ (val) }

/*

 * Read an atomic64_t non-atomically.

 *

 * This is intended to be used in cases where a subsequent atomic operation

 * will handle the torn value, and can be used to prime the first iteration

 * of unconditional try_cmpxchg() loops, e.g.:

 *

 * 	s64 val = arch_atomic64_read_nonatomic(v);

 * 	do { } while (!arch_atomic64_try_cmpxchg(v, &val, val OP i);

 *

 * This is NOT safe to use where the value is not always checked by a

 * subsequent atomic operation, such as in conditional try_cmpxchg() loops

 * that can break before the atomic operation, e.g.:

 *

 * 	s64 val = arch_atomic64_read_nonatomic(v);

 * 	do {

 * 		if (condition(val))

 * 			break;

 * 	} while (!arch_atomic64_try_cmpxchg(v, &val, val OP i);

 */

static __always_inline s64 arch_atomic64_read_nonatomic(const atomic64_t *v)

{

	/* See comment in arch_atomic_read(). */

	return __READ_ONCE(v->counter);

}

#define __ATOMIC64_DECL(sym) void atomic64_##sym(atomic64_t *, ...)

#ifndef ATOMIC64_EXPORT

#define ATOMIC64_DECL_ONE __ATOMIC64_DECL