[PATCH] stacktrace: don't crash on invalid stack trace structs

[Johannes Berg <johannes@sipsolutions.net>]

This patch makes the stacktrace printout code warn when the entries
pointer is unset rather than crashing when trying to access it in an
attempt to make it a bit more robust.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
---
I was saving a stacktrace into an skb and forgot to copy it across skb
copies... Not sure if you want this, I have since fixed the code, but it
would have been easier had the kernel not crashed in an interrupt.

--- everything.orig/kernel/stacktrace.c	2008-05-04 14:02:14.000000000 +0200
+++ everything/kernel/stacktrace.c	2008-05-04 14:02:24.000000000 +0200
@@ -13,6 +13,9 @@ void print_stack_trace(struct stack_trac
 {
 	int i, j;
 
+	if (WARN_ON(!trace->entries))
+		return;
+
 	for (i = 0; i < trace->nr_entries; i++) {
 		unsigned long ip = trace->entries[i];