diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 793b150..416ba80 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -213,6 +213,8 @@
 	return 0;
 }
 
+#define PROC_MAP_PARSE_TIMEOUT	(500 * 1000000ULL)
+
 int perf_event__synthesize_mmap_events(struct perf_tool *tool,
 				       union perf_event *event,
 				       pid_t pid, pid_t tgid,
@@ -222,6 +224,8 @@
 {
 	char filename[PATH_MAX];
 	FILE *fp;
+	unsigned long long t;
+	bool truncation = false;
 	int rc = 0;
 
 	if (machine__is_default_guest(machine))
@@ -240,6 +244,7 @@
 	}
 
 	event->header.type = PERF_RECORD_MMAP2;
+	t = rdclock();
 
 	while (1) {
 		char bf[BUFSIZ];
@@ -253,6 +258,12 @@
 		if (fgets(bf, sizeof(bf), fp) == NULL)
 			break;
 
+		if ((rdclock() - t) > PROC_MAP_PARSE_TIMEOUT) {
+			pr_warning("Reading %s time out.\n", filename);
+			truncation = true;
+			goto out;
+		}
+
 		/* ensure null termination since stack will be reused. */
 		strcpy(execname, "");
 
@@ -301,6 +312,10 @@
 			event->header.misc |= PERF_RECORD_MISC_MMAP_DATA;
 		}
 
+out:
+		if (truncation)
+			event->header.misc |= PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT;
+
 		if (!strcmp(execname, ""))
 			strcpy(execname, anonstr);
 
@@ -319,6 +334,9 @@
 			rc = -1;
 			break;
 		}
+
+		if (truncation)
+			break;
 	}
 
 	fclose(fp);
diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
index 5dc51ad..39868f5 100644
--- a/tools/perf/util/event.h
+++ b/tools/perf/util/event.h
@@ -265,6 +265,7 @@
 	u32 nr_unknown_id;
 	u32 nr_unprocessable_samples;
 	u32 nr_auxtrace_errors[PERF_AUXTRACE_ERROR_MAX];
+	u32 nr_proc_map_timeout;
 };
 
 struct attr_event {
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index c371336..2d882fd 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1064,6 +1064,8 @@
 	case PERF_RECORD_MMAP:
 		return tool->mmap(tool, event, sample, machine);
 	case PERF_RECORD_MMAP2:
+		if (event->header.misc & PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT)
+			++evlist->stats.nr_proc_map_timeout;
 		return tool->mmap2(tool, event, sample, machine);
 	case PERF_RECORD_COMM:
 		return tool->comm(tool, event, sample, machine);
@@ -1360,6 +1362,15 @@
 		ui__warning("%u out of order events recorded.\n", oe->nr_unordered_events);
 
 	events_stats__auxtrace_error_warn(stats);
+
+	if (stats->nr_proc_map_timeout != 0) {
+		ui__warning("%d map information files for pre-existing threads were\n"
+			    "not processed, if there are samples for addresses they\n"
+			    "will not be resolved, you may find out which are these\n"
+			    "threads by running with -v and redirecting the output\n"
+			    "to a file.\n",
+			    stats->nr_proc_map_timeout);
+	}
 }
 
 static int perf_session__flush_thread_stack(struct thread *thread,