perf tools: Don't use parent comm if not set at fork time

As the parent comm then is worthless, confusing users about the
thread where the sample really happened, leading to think that
the sample happened in the parent, not where it really happened,
in the children of a thread for which a PERF_RECORD_COMM event
was not received.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1266627727-19715-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 13 insertions, 6 deletions

diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index 634b7f7140d5..9e8995eaf2b6 100644
--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -36,7 +36,10 @@ int thread__set_comm(struct thread *self, const char *comm)
         if (self->comm)
                 free(self->comm);
         self->comm = strdup(comm);
-        return self->comm ? 0 : -ENOMEM;
+        if (self->comm == NULL)
+                return -ENOMEM;
+        self->comm_set = true;
+        return 0;
 }
 
 int thread__comm_len(struct thread *self)
@@ -255,11 +258,14 @@ int thread__fork(struct thread *self, struct thread *parent)
 {
         int i;
 
-        if (self->comm)
-                free(self->comm);
-        self->comm = strdup(parent->comm);
-        if (!self->comm)
-                return -ENOMEM;
+        if (parent->comm_set) {
+                if (self->comm)
+                        free(self->comm);
+                self->comm = strdup(parent->comm);
+                if (!self->comm)
+                        return -ENOMEM;
+                self->comm_set = true;
+        }
 
         for (i = 0; i < MAP__NR_TYPES; ++i)
                 if (map_groups__clone(&self->mg, &parent->mg, i) < 0)
diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
index 56f317b8a06c..0a28f39de545 100644
--- a/tools/perf/util/thread.h
+++ b/tools/perf/util/thread.h
@@ -15,6 +15,7 @@ struct thread {
         struct map_groups       mg;
         pid_t                   pid;
         char                    shortname[3];
+        bool                    comm_set;
         char                    *comm;
         int                     comm_len;
 };