linux-kernel - [PATCH 2/3] perf tools: Make fork event processing more resilient

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Date:	Wed, 19 Aug 2015 17:29:20 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Jiri Olsa <jolsa@...nel.org>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	mingo@...nel.org
Subject: [PATCH 2/3] perf tools: Make fork event processing more resilient

When processing a fork event, the tools lookup the parent
thread by its tid.  In a couple of cases, it is possible
for that thread to have the wrong pid.  That can happen
if the data is being processed out of order, or if the
(fork) event that would have removed the erroneous
thread was lost.  Assume the latter case, print a dump
message, remove the erroneous thread, create a new one
with the correct pid, and keep going.

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
 tools/perf/util/machine.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 7ff682770fdb..f1a4c833121e 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1387,6 +1387,24 @@ int machine__process_fork_event(struct machine *machine, union perf_event *event
 							event->fork.ptid);
 	int err = 0;
 
+	if (dump_trace)
+		perf_event__fprintf_task(event, stdout);
+
+	/*
+	 * There may be an existing thread that is not actually the parent,
+	 * either because we are processing events out of order, or because the
+	 * (fork) event that would have removed the thread was lost. Assume the
+	 * latter case and continue on as best we can.
+	 */
+	if (parent->pid_ != (pid_t)event->fork.ppid) {
+		dump_printf("removing erroneous parent thread %d/%d\n",
+			    parent->pid_, parent->tid);
+		machine__remove_thread(machine, parent);
+		thread__put(parent);
+		parent = machine__findnew_thread(machine, event->fork.ppid,
+						 event->fork.ptid);
+	}
+
 	/* if a thread currently exists for the thread id remove it */
 	if (thread != NULL) {
 		machine__remove_thread(machine, thread);
@@ -1395,8 +1413,6 @@ int machine__process_fork_event(struct machine *machine, union perf_event *event
 
 	thread = machine__findnew_thread(machine, event->fork.pid,
 					 event->fork.tid);
-	if (dump_trace)
-		perf_event__fprintf_task(event, stdout);
 
 	if (thread == NULL || parent == NULL ||
 	    thread__fork(thread, parent, sample->time) < 0) {
-- 
1.9.1

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