perf tools: Fix synthesizing fork_event.ppid for non-main thread

Commit ca6c41c59b9 sets the ppid based on what is read from the
/proc/pid/status file when synthesizing fork events.

This is correct thing to do for new processes but not threads of a
process.

Fix ppid for threads to be the main thread when synthesizing fork events
(ie., assume main thread spawned all sub-threads in a process).

Reported-by: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Signed-off-by: David Ahern <david.ahern@oracle.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Link: http://lkml.kernel.org/r/1428598107-178999-1-git-send-email-david.ahern@oracle.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 5516236df6ab..9d0985131252 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -183,8 +183,18 @@ static int perf_event__synthesize_fork(struct perf_tool *tool,
 {
         memset(&event->fork, 0, sizeof(event->fork) + machine->id_hdr_size);
 
-        event->fork.ppid = ppid;
-        event->fork.ptid = ppid;
+        /*
+         * for main thread set parent to ppid from status file. For other
+         * threads set parent pid to main thread. ie., assume main thread
+         * spawns all threads in a process
+        */
+        if (tgid == pid) {
+                event->fork.ppid = ppid;
+                event->fork.ptid = ppid;
+        } else {
+                event->fork.ppid = tgid;
+                event->fork.ptid = tgid;
+        }
         event->fork.pid  = tgid;
         event->fork.tid  = pid;
         event->fork.header.type = PERF_RECORD_FORK;