powerpc: Hard disable interrupts in xmon

xmon only soft disables interrupts. This seems like a bad idea - we
certainly don't want decrementer and PMU exceptions going off when
we are debugging something inside xmon.

This issue was uncovered when the hard lockup detector went off
inside xmon. To ensure we wont get a spurious hard lockup warning,
I also call touch_nmi_watchdog() when exiting xmon.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/xmon/xmon.c

@@ -24,6 +24,7 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/bug.h>
+#include <linux/nmi.h>
 
 #include <asm/ptrace.h>
 #include <asm/string.h>
@@ -374,6 +375,7 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
 #endif
 
 	local_irq_save(flags);
+	hard_irq_disable();
 
 	bp = in_breakpoint_table(regs->nip, &offset);
 	if (bp != NULL) {
@@ -558,6 +560,7 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
 #endif
 	insert_cpu_bpts();
 
+	touch_nmi_watchdog();
 	local_irq_restore(flags);
 
 	return cmd != 'X' && cmd != EOF;