Add a check for the stack canary when we oops, similar to x86. This should make
it clear that we overran our stack:

Unable to handle kernel paging request for data at address 0x24652f63700ac689
Faulting instruction address: 0xc000000000063d24
Thread overran stack, or stack corrupted

Signed-off-by: Anton Blanchard <redacted>
---

Index: powerpc.git/arch/powerpc/mm/fault.c
===================================================================

--- powerpc.git.orig/arch/powerpc/mm/fault.c	2010-08-25 08:41:08.230086186 +1000
+++ powerpc.git/arch/powerpc/mm/fault.c	2010-08-25 09:12:38.276553103 +1000

@@ -30,6 +30,7 @@
 #include <linux/kprobes.h>
 #include <linux/kdebug.h>
 #include <linux/perf_event.h>
+#include <linux/magic.h>
 
 #include <asm/firmware.h>
 #include <asm/page.h>

@@ -385,6 +386,7 @@ do_sigbus:
 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 {
 	const struct exception_table_entry *entry;
+	unsigned long *stackend;
 
 	/* Are we prepared to handle this fault?  */
 	if ((entry = search_exception_tables(regs->nip)) != NULL) {

@@ -413,5 +415,9 @@ void bad_page_fault(struct pt_regs *regs
 	printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
 		regs->nip);
 
+	stackend = end_of_stack(current);
+	if (current != &init_task && *stackend != STACK_END_MAGIC)
+		printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");