3 files changed, 66 insertions, 6 deletions

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 5b8087728f28..5484fa4385fc 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -272,6 +272,52 @@ void machines__set_id_hdr_size(struct machines *machines, u16 id_hdr_size)
 	return;
 }
 
+static void machine__update_thread_pid(struct machine *machine,
+				       struct thread *th, pid_t pid)
+{
+	struct thread *leader;
+
+	if (pid == th->pid_ || pid == -1 || th->pid_ != -1)
+		return;
+
+	th->pid_ = pid;
+
+	if (th->pid_ == th->tid)
+		return;
+
+	leader = machine__findnew_thread(machine, th->pid_, th->pid_);
+	if (!leader)
+		goto out_err;
+
+	if (!leader->mg)
+		leader->mg = map_groups__new();
+
+	if (!leader->mg)
+		goto out_err;
+
+	if (th->mg == leader->mg)
+		return;
+
+	if (th->mg) {
+		/*
+		 * Maps are created from MMAP events which provide the pid and
+		 * tid.  Consequently there never should be any maps on a thread
+		 * with an unknown pid.  Just print an error if there are.
+		 */
+		if (!map_groups__empty(th->mg))
+			pr_err("Discarding thread maps for %d:%d\n",
+			       th->pid_, th->tid);
+		map_groups__delete(th->mg);
+	}
+
+	th->mg = map_groups__get(leader->mg);
+
+	return;
+
+out_err:
+	pr_err("Failed to join map groups for %d:%d\n", th->pid_, th->tid);
+}
+
 static struct thread *__machine__findnew_thread(struct machine *machine,
 						pid_t pid, pid_t tid,
 						bool create)
@@ -285,10 +331,10 @@ static struct thread *__machine__findnew_thread(struct machine *machine,
 	 * so most of the time we dont have to look up
 	 * the full rbtree:
 	 */
-	if (machine->last_match && machine->last_match->tid == tid) {
-		if (pid != -1 && pid != machine->last_match->pid_)
-			machine->last_match->pid_ = pid;
-		return machine->last_match;
+	th = machine->last_match;
+	if (th && th->tid == tid) {
+		machine__update_thread_pid(machine, th, pid);
+		return th;
 	}
 
 	while (*p != NULL) {
@@ -297,8 +343,7 @@ static struct thread *__machine__findnew_thread(struct machine *machine,
 
 		if (th->tid == tid) {
 			machine->last_match = th;
-			if (pid != -1 && pid != th->pid_)
-				th->pid_ = pid;
+			machine__update_thread_pid(machine, th, pid);
 			return th;
 		}
 
diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
index 25c571f4cba6..7af14807ee90 100644
--- a/tools/perf/util/map.c
+++ b/tools/perf/util/map.c
@@ -454,6 +454,20 @@ void map_groups__exit(struct map_groups *mg)
 	}
 }
 
+bool map_groups__empty(struct map_groups *mg)
+{
+	int i;
+
+	for (i = 0; i < MAP__NR_TYPES; ++i) {
+		if (maps__first(&mg->maps[i]))
+			return false;
+		if (!list_empty(&mg->removed_maps[i]))
+			return false;
+	}
+
+	return true;
+}
+
 struct map_groups *map_groups__new(void)
 {
 	struct map_groups *mg = malloc(sizeof(*mg));
diff --git a/tools/perf/util/map.h b/tools/perf/util/map.h
index 7758c72522ef..5806a906198b 100644
--- a/tools/perf/util/map.h
+++ b/tools/perf/util/map.h
@@ -66,6 +66,7 @@ struct map_groups {
 
 struct map_groups *map_groups__new(void);
 void map_groups__delete(struct map_groups *mg);
+bool map_groups__empty(struct map_groups *mg);
 
 static inline struct map_groups *map_groups__get(struct map_groups *mg)
 {