[POWERPC] Handle recursive oopses

Handle recursive oopses, like on x86. We had a few cases recently where
we locked up in oops printing and didnt make it into crashdump.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/traps.c

@@ -108,23 +108,38 @@ static void pmac_backlight_unblank(void)
 static inline void pmac_backlight_unblank(void) { }
 #endif
 
-static DEFINE_SPINLOCK(die_lock);
-
 int die(const char *str, struct pt_regs *regs, long err)
 {
+	static struct {
+		spinlock_t lock;
+		u32 lock_owner;
+		int lock_owner_depth;
+	} die = {
+		.lock =			__SPIN_LOCK_UNLOCKED(die.lock),
+		.lock_owner =		-1,
+		.lock_owner_depth =	0
+	};
 	static int die_counter;
+	unsigned long flags;
 
 	if (debugger(regs))
 		return 1;
 
 	oops_enter();
 
+	if (die.lock_owner != raw_smp_processor_id()) {
 		console_verbose();
-	spin_lock_irq(&die_lock);
+		spin_lock_irqsave(&die.lock, flags);
+		die.lock_owner = smp_processor_id();
+		die.lock_owner_depth = 0;
 		bust_spinlocks(1);
 		if (machine_is(powermac))
 			pmac_backlight_unblank();
+	} else {
+		local_save_flags(flags);
+	}
 
+	if (++die.lock_owner_depth < 3) {
 		printk("Oops: %s, sig: %ld [#%d]\n", str, err, ++die_counter);
 #ifdef CONFIG_PREEMPT
 		printk("PREEMPT ");
@@ -142,8 +157,13 @@ int die(const char *str, struct pt_regs *regs, long err)
 
 		print_modules();
 		show_regs(regs);
+	} else {
+		printk("Recursive die() failure, output suppressed\n");
+	}
+
 	bust_spinlocks(0);
-	spin_unlock_irq(&die_lock);
+	die.lock_owner = -1;
+	spin_unlock_irqrestore(&die.lock, flags);
 
 	if (kexec_should_crash(current) ||
 		kexec_sr_activated(smp_processor_id()))