i386: Terminate backtrace fallback early if unwinder stack pointer is zero

Cc: jbeulich@novell.com
Signed-off-by: Andi Kleen <ak@suse.de>

---
 arch/i386/kernel/traps.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux/arch/i386/kernel/traps.c
===================================================================
--- linux.orig/arch/i386/kernel/traps.c
+++ linux/arch/i386/kernel/traps.c
@@ -197,6 +197,8 @@ void dump_trace(struct task_struct *task
 				if (UNW_SP(&info) >= PAGE_OFFSET) {
 					ops->warning(data, "Leftover inexact backtrace:\n");
 					stack = (void *)UNW_SP(&info);
+					if (!stack)
+						return;
 				} else
 					ops->warning(data, "Full inexact backtrace again:\n");
 			} else if (call_trace >= 1)