[PATCH] mutex subsystem, add include/asm-i386/mutex.h

/*

 * Assembly implementation of the mutex fastpath, based on atomic

 * decrement/increment.

 *

 * started by Ingo Molnar:

 *

 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>

 */

#ifndef _ASM_MUTEX_H

#define _ASM_MUTEX_H

/**

 *  __mutex_fastpath_lock - try to take the lock by moving the count

 *                          from 1 to a 0 value

 *  @count: pointer of type atomic_t

 *  @fn: function to call if the original value was not 1

 *

 * Change the count from 1 to a value lower than 1, and call <fn> if it

 * wasn't 1 originally. This function MUST leave the value lower than 1

 * even when the "1" assertion wasn't true.

 */

#define __mutex_fastpath_lock(count, fail_fn)				\

do {									\

	unsigned int dummy;						\

									\

	typecheck(atomic_t *, count);					\

	typecheck_fn(fastcall void (*)(atomic_t *), fail_fn);		\

									\

	__asm__ __volatile__(						\

		LOCK	"   decl (%%eax)	\n"			\

			"   js "#fail_fn"	\n"			\

									\

		:"=a" (dummy)						\

		: "a" (count)						\

		: "memory", "ecx", "edx");				\

} while (0)

/**

 *  __mutex_fastpath_lock_retval - try to take the lock by moving the count

 *                                 from 1 to a 0 value

 *  @count: pointer of type atomic_t

 *  @fail_fn: function to call if the original value was not 1

 *

 * Change the count from 1 to a value lower than 1, and call <fail_fn> if it

 * wasn't 1 originally. This function returns 0 if the fastpath succeeds,

 * or anything the slow path function returns

 */

static inline int

__mutex_fastpath_lock_retval(atomic_t *count,

			     int fastcall (*fail_fn)(atomic_t *))

{

	if (unlikely(atomic_dec_return(count) < 0))

		return fail_fn(count);

	else

		return 0;

}

/**

 *  __mutex_fastpath_unlock - try to promote the mutex from 0 to 1

 *  @count: pointer of type atomic_t

 *  @fail_fn: function to call if the original value was not 0

 *

 * try to promote the mutex from 0 to 1. if it wasn't 0, call <fail_fn>.

 * In the failure case, this function is allowed to either set the value

 * to 1, or to set it to a value lower than 1.

 *

 * If the implementation sets it to a value of lower than 1, the

 * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs

 * to return 0 otherwise.

 */

#define __mutex_fastpath_unlock(count, fail_fn)				\

do {									\

	unsigned int dummy;						\

									\

	typecheck(atomic_t *, count);					\

	typecheck_fn(fastcall void (*)(atomic_t *), fail_fn);		\

									\

	__asm__ __volatile__(						\

		LOCK	"   incl (%%eax)	\n"			\

			"   jle "#fail_fn"	\n"			\

									\

		:"=a" (dummy)						\

		: "a" (count)						\

		: "memory", "ecx", "edx");				\

} while (0)

#define __mutex_slowpath_needs_to_unlock()	1

/**

 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting

 *

 *  @count: pointer of type atomic_t

 *  @fail_fn: fallback function

 *

 * Change the count from 1 to a value lower than 1, and return 0 (failure)

 * if it wasn't 1 originally, or return 1 (success) otherwise. This function

 * MUST leave the value lower than 1 even when the "1" assertion wasn't true.

 * Additionally, if the value was < 0 originally, this function must not leave

 * it to 0 on failure.

 */

static inline int

__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))

{

	/*

	 * We have two variants here. The cmpxchg based one is the best one

	 * because it never induce a false contention state.  It is included

	 * here because architectures using the inc/dec algorithms over the

	 * xchg ones are much more likely to support cmpxchg natively.

	 *

	 * If not we fall back to the spinlock based variant - that is

	 * just as efficient (and simpler) as a 'destructive' probing of

	 * the mutex state would be.

	 */

#ifdef __HAVE_ARCH_CMPXCHG

	if (likely(atomic_cmpxchg(count, 1, 0)) == 1)

		return 1;

	return 0;

#else

	return fail_fn(count);

#endif

}

#endif