[PATCH] Fix machine check handler on x86-64

This fixes a bug in the new machine check handler on x86-64.

One nasty part was that when you got an MCE during boot up
then it would not always print it on the screen, but still
panic because it attempted to kill the idle task.

This patch does:
 - Always use KERN_EMERG when printing MCEs
 - Always panic and print on screen before killing idle loop
   or init.

arch/x86_64/kernel/mce.c

@@ -71,17 +71,19 @@ static void mce_log(struct mce *mce)
 
 static void print_mce(struct mce *m)
 {
-	printk("CPU %d: Machine Check Exception: %16Lx Bank %d: %016Lx\n",
+	printk(KERN_EMERG 
+	       "CPU %d: Machine Check Exception: %16Lx Bank %d: %016Lx\n",
 	       m->cpu, m->mcgstatus, m->bank, m->status);
 	if (m->rip) {
-		printk("RIP%s %02x:<%016Lx> ",
+		printk(KERN_EMERG 
+		       "RIP%s %02x:<%016Lx> ",
 		       !(m->mcgstatus & MCG_STATUS_EIPV) ? " !INEXACT!" : "",
 		       m->cs, m->rip);
 		if (m->cs == __KERNEL_CS)
 			print_symbol("{%s}", m->rip);
 		printk("\n");
 	}
-	printk("TSC %Lx ", m->tsc); 
+	printk(KERN_EMERG "TSC %Lx ", m->tsc); 
 	if (m->addr)
 		printk("ADDR %Lx ", m->addr);
 	if (m->misc)
@@ -177,9 +179,14 @@ void do_machine_check(struct pt_regs * regs, long error_code)
 		int user_space = (m.rip && (m.cs & 3));
 		
 		/* When the machine was in user space and the CPU didn't get
-		   confused it's normally not necessary to panic, unless you are 
-		   paranoid (tolerant == 0) */ 
-		if (!user_space && (panic_on_oops || tolerant < 2))
+		   confused it's normally not necessary to panic, unless you 
+		   are paranoid (tolerant == 0)
+
+		   RED-PEN could be more tolerant for MCEs in idle,
+		   but most likely they occur at boot anyways, where
+		   it is best to just halt the machine. */
+		if ((!user_space && (panic_on_oops || tolerant < 2)) ||
+		    (unsigned)current->pid <= 1)
 			mce_panic("Uncorrected machine check", &m, mcestart);
 
 		/* do_exit takes an awful lot of locks and has as slight risk