perf tools: Check if callchain is corrupted

We faced segmentation fault on perf top -G at very high sampling rate
due to a corrupted callchain. While the root cause was not revealed (I
failed to figure it out), this patch tries to protect us from the
segfault on such cases.
Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung.kim@lge.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sunjin Yang <fan4326@gmail.com>
Link: http://lkml.kernel.org/r/1338443007-24857-2-git-send-email-namhyung.kim@lge.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

include/linux/perf_event.h

@@ -555,6 +555,8 @@ enum perf_event_type {
 	PERF_RECORD_MAX,			/* non-ABI */
 };
 
+#define PERF_MAX_STACK_DEPTH		255
+
 enum perf_callchain_context {
 	PERF_CONTEXT_HV			= (__u64)-32,
 	PERF_CONTEXT_KERNEL		= (__u64)-128,
@@ -609,8 +611,6 @@ struct perf_guest_info_callbacks {
 #include <linux/sysfs.h>
 #include <asm/local.h>
 
-#define PERF_MAX_STACK_DEPTH		255
-
 struct perf_callchain_entry {
 	__u64				nr;
 	__u64				ip[PERF_MAX_STACK_DEPTH];

tools/perf/util/session.c

@@ -300,6 +300,11 @@ int machine__resolve_callchain(struct machine *self,
 
 	callchain_cursor_reset(&callchain_cursor);
 
+	if (chain->nr > PERF_MAX_STACK_DEPTH) {
+		pr_warning("corrupted callchain. skipping...\n");
+		return 0;
+	}
+
 	for (i = 0; i < chain->nr; i++) {
 		u64 ip;
 		struct addr_location al;
@@ -318,7 +323,14 @@ int machine__resolve_callchain(struct machine *self,
 			case PERF_CONTEXT_USER:
 				cpumode = PERF_RECORD_MISC_USER;	break;
 			default:
-				break;
+				pr_debug("invalid callchain context: "
+					 "%"PRId64"\n", (s64) ip);
+				/*
+				 * It seems the callchain is corrupted.
+				 * Discard all.
+				 */
+				callchain_cursor_reset(&callchain_cursor);
+				return 0;
 			}
 			continue;
 		}