uml: use barrier() instead of mb()

#include "sysdep/sigcontext.h"

#include "user.h"

/* Copied from linux/compiler-gcc.h since we can't include it directly */

#define barrier() __asm__ __volatile__("": : :"memory")

/*

 * These are the asynchronous signals.  SIGPROF is excluded because we want to

 * be able to profile all of UML, not just the non-critical sections.  If

#define SIGVTALRM_BIT 1

#define SIGVTALRM_MASK (1 << SIGVTALRM_BIT)

/*

 * These are used by both the signal handlers and

 * block/unblock_signals.  I don't want modifications cached in a

 * register - they must go straight to memory.

 */

static volatile int signals_enabled = 1;

static volatile int pending = 0;

static int signals_enabled;

static unsigned int pending;

void sig_handler(int sig, struct sigcontext *sc)

{

	 * This might matter if gcc figures out how to inline this and

	 * decides to shuffle this code into the caller.

	 */

	mb();

	barrier();

}

void unblock_signals(void)

		 * Setting signals_enabled and reading pending must

		 * happen in this order.

		 */

		mb();

		barrier();

		save_pending = pending;

		if (save_pending == 0) {

			/*

			 * This must return with signals enabled, so

			 * this barrier ensures that writes are

			 * flushed out before the return.  This might

			 * matter if gcc figures out how to inline

			 * this (unlikely, given its size) and decides

			 * to shuffle this code into the caller.

			 */

			mb();

		if (save_pending == 0)

			return;

		}

		pending = 0;