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)
 {