[tip:perf/core] perf tools: Make fork event processing more resilient

[tip-bot for Adrian Hunter]

Commit-ID:  5cb73340d92a716fd2776700742c3558206ae298
Gitweb:     http://git.kernel.org/tip/5cb73340d92a716fd2776700742c3558206ae298
Author:     Adrian Hunter <adrian.hunter@xxxxxxxxx>
AuthorDate: Wed, 19 Aug 2015 17:29:20 +0300
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Wed, 19 Aug 2015 14:15:25 -0300

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.

Reported-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Tested-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1439994561-27436-3-git-send-email-adrian.hunter@xxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 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 7ff6827..f1a4c83 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) {
--
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