[PATCH] smp_call_function needs mb()

We really need a memory barrier in smp_call_function(), so that the
other cpu's get the updated value when they get IPI'd immediately
afterwards.

This seems to be true on some old (and arguably broken) hardware where
the IPI generation and reception doesn't synchronize enough.

arch/i386/kernel/smp.c

@@ -522,7 +522,8 @@ int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
 
 	spin_lock(&call_lock);
 	call_data = &data;
-	wmb();
+	mb();
+	
 	/* Send a message to all other CPUs and wait for them to respond */
 	send_IPI_allbutself(CALL_FUNCTION_VECTOR);