xen: Use wmb instead of rmb in xen_evtchn_do_upcall().

From: Isaku Yamahata <[email protected]>

This patch is ported one from 534:77db69c38249 of linux-2.6.18-xen.hg. Use wmb instead of rmb to enforce ordering between evtchn_upcall_pending and evtchn_pending_sel stores
in xen_evtchn_do_upcall().

---
drivers/xen/events.c | 3 +--

1 file changed, 1 insertion(+), 2 deletions(-)

===================================================================

@@ -529,7 +529,7 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
 

#ifndef CONFIG_X86 /* No need for a barrier -- XCHG is a barrier on x86. */
		/* Clear master flag /before/ clearing selector flag. */
-		rmb();
+		wmb();
#endif
		pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);
		while (pending_words != 0) {

1.5.3