x86: don't save unreliable stack trace entries

Currently, there is no way for print_stack_trace() to determine whether
a given stack trace entry was deemed reliable or not, simply because
save_stack_trace() does not record this information. (Perhaps needless
to say, this makes the saved stack traces A LOT harder to read, and
probably with no other benefits, since debugging features that use
save_stack_trace() most likely also require frame pointers, etc.)

This patch reverts to the old behaviour of only recording the reliable trace
entries for saved stack traces.
Signed-off-by: NVegard Nossum <vegardno@ifi.uio.no>
Acked-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/stacktrace.c

@@ -25,6 +25,8 @@ static int save_stack_stack(void *data, char *name)
 static void save_stack_address(void *data, unsigned long addr, int reliable)
 {
 	struct stack_trace *trace = data;
+	if (!reliable)
+		return;
 	if (trace->skip > 0) {
 		trace->skip--;
 		return;
@@ -37,6 +39,8 @@ static void
 save_stack_address_nosched(void *data, unsigned long addr, int reliable)
 {
 	struct stack_trace *trace = (struct stack_trace *)data;
+	if (!reliable)
+		return;
 	if (in_sched_functions(addr))
 		return;
 	if (trace->skip > 0) {