linux-kernel - [PATCH] perf tools: Fix use of wrong event when processing exit events

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Message-Id: <1439888825-27708-1-git-send-email-adrian.hunter@intel.com>
Date:	Tue, 18 Aug 2015 12:07:05 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>
Subject: [PATCH] perf tools: Fix use of wrong event when processing exit events

In a couple of cases the 'comm' member of 'union event' has
been used instead of the correct member ('fork') when processing
exit events.

In the cases where it has been used incorrectly, only the 'pid'
and 'tid' are affected.  The 'pid' value would be correct anyway
because it is in the same position in 'comm' and 'fork' events,
but the 'tid' would have been incorrectly assigned from 'ppid'.
However, for exit events, the kernel puts the current task in
the 'ppid' and 'ttid' which is the same as the exiting task.
That is 'ppid' == 'pid' and if the task is not multi-threaded,
'pid' == 'tid' i.e. the data goes wrong only when tracing
multi-threaded programs.

It is hard to find an example of how this would produce an
error in practice.  There are 3 occurences of the fix:
1. perf script is only affected if !sample_id_all which only
happens on old kernels
2. intel_pt is only affected when decoding without timestamps
and would probably still decode correctly - the exit event is
only used to flush out data which anyway gets flushed at the
end of the session
3. intel_bts also uses the exit event to flush data which
would probably not cause errors as it would get flushed at
the end of the session instead

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
 tools/perf/builtin-script.c | 4 ++--
 tools/perf/util/intel-bts.c | 2 +-
 tools/perf/util/intel-pt.c  | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index 105332e950a9..17030c6c64b6 100644
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -739,8 +739,8 @@ static int process_exit_event(struct perf_tool *tool,
 	if (!evsel->attr.sample_id_all) {
 		sample->cpu = 0;
 		sample->time = 0;
-		sample->tid = event->comm.tid;
-		sample->pid = event->comm.pid;
+		sample->tid = event->fork.tid;
+		sample->pid = event->fork.pid;
 	}
 	print_sample_start(sample, thread, evsel);
 	perf_event__fprintf(event, stdout);
diff --git a/tools/perf/util/intel-bts.c b/tools/perf/util/intel-bts.c
index dce99cfb1309..09d142b362fa 100644
--- a/tools/perf/util/intel-bts.c
+++ b/tools/perf/util/intel-bts.c
@@ -623,7 +623,7 @@ static int intel_bts_process_event(struct perf_session *session,
 	if (err)
 		return err;
 	if (event->header.type == PERF_RECORD_EXIT) {
-		err = intel_bts_process_tid_exit(bts, event->comm.tid);
+		err = intel_bts_process_tid_exit(bts, event->fork.tid);
 		if (err)
 			return err;
 	}
diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
index 2a4a4120473b..ef2fb13f1dfa 100644
--- a/tools/perf/util/intel-pt.c
+++ b/tools/perf/util/intel-pt.c
@@ -1464,7 +1464,7 @@ static int intel_pt_process_event(struct perf_session *session,
 	if (pt->timeless_decoding) {
 		if (event->header.type == PERF_RECORD_EXIT) {
 			err = intel_pt_process_timeless_queues(pt,
-							       event->comm.tid,
+							       event->fork.tid,
 							       sample->time);
 		}
 	} else if (timestamp) {
-- 
1.9.1

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