[PATCH 1/2] perf session: Add option to copy events when queueing

[Alexander Yarygin]

From: David Ahern <dsahern@xxxxxxxxx>

When processing events the session code has an ordered samples queue which is
used to time-sort events coming in across multiple mmaps. At a later point in
time samples on the queue are flushed up to some timestamp at which point the
event is actually processed.

When analyzing events live (ie., record/analysis path in the same command)
there is a race that leads to corrupted events and parse errors which cause
perf to terminate. The problem is that when the event is placed in the ordered
samples queue it is only a reference to the event which is really sitting in
the mmap buffer. Even though the event is queued for later processing the mmap
tail pointer is updated which indicates to the kernel that the event has been
processed. The race is flushing the event from the queue before it gets
overwritten by some other event. For commands trying to process events live
(versus just writing to a file) and processing a high rate of events this leads
to parse failures and perf terminates.

Examples hitting this problem are 'perf kvm stat live', especially with nested
VMs which generate 100,000+ traces per second, and a command processing
scheduling events with a high rate of context switching -- e.g., running
'perf bench sched pipe'.

This patch offers live commands an option to copy the event when it is placed in
the ordered samples queue.

Signed-off-by: David Ahern <dsahern@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Namhyung Kim <namhyung.kim@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Signed-off-by: Alexander Yarygin <yarygin@xxxxxxxxxxxxxxxxxx>
---
 tools/perf/util/ordered-events.c | 12 +++++++++---
 tools/perf/util/ordered-events.h |  2 +-
 tools/perf/util/session.c        | 12 +++++++++---
 tools/perf/util/session.h        |  1 +
 4 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/tools/perf/util/ordered-events.c b/tools/perf/util/ordered-events.c
index 706ce1a..5b51de5 100644
--- a/tools/perf/util/ordered-events.c
+++ b/tools/perf/util/ordered-events.c
@@ -140,11 +140,15 @@ static int __ordered_events__flush(struct perf_session *s,
 			break;
 
 		ret = perf_evlist__parse_sample(s->evlist, iter->event, &sample);
-		if (ret)
+		if (ret) {
 			pr_err("Can't parse sample, err = %d\n", ret);
-		else {
+			if (s->copy_on_queue)
+				free(iter->event);
+		} else {
 			ret = perf_session__deliver_event(s, iter->event, &sample, tool,
 							  iter->file_offset);
+			if (s->copy_on_queue)
+				free(iter->event);
 			if (ret)
 				return ret;
 		}
@@ -233,13 +237,15 @@ void ordered_events__init(struct ordered_events *oe)
 	oe->cur_alloc_size = 0;
 }
 
-void ordered_events__free(struct ordered_events *oe)
+void ordered_events__free(struct perf_session *s, struct ordered_events *oe)
 {
 	while (!list_empty(&oe->to_free)) {
 		struct ordered_event *event;
 
 		event = list_entry(oe->to_free.next, struct ordered_event, list);
 		list_del(&event->list);
+		if (s->copy_on_queue)
+			free(event->event);
 		free(event);
 	}
 }
diff --git a/tools/perf/util/ordered-events.h b/tools/perf/util/ordered-events.h
index 3b2f205..a156b0e 100644
--- a/tools/perf/util/ordered-events.h
+++ b/tools/perf/util/ordered-events.h
@@ -41,7 +41,7 @@ void ordered_events__delete(struct ordered_events *oe, struct ordered_event *eve
 int ordered_events__flush(struct perf_session *s, struct perf_tool *tool,
 			  enum oe_flush how);
 void ordered_events__init(struct ordered_events *oe);
-void ordered_events__free(struct ordered_events *oe);
+void ordered_events__free(struct perf_session *s, struct ordered_events *oe);
 
 static inline
 void ordered_events__set_alloc_size(struct ordered_events *oe, u64 size)
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 6d2d50d..40d3aec 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -542,7 +542,13 @@ int perf_session_queue_event(struct perf_session *s, union perf_event *event,
 		return -ENOMEM;
 
 	new->file_offset = file_offset;
-	new->event = event;
+
+	if (s->copy_on_queue) {
+		new->event = malloc(event->header.size);
+		memcpy(new->event, event, event->header.size);
+	} else
+		new->event = event;
+
 	return 0;
 }
 
@@ -1164,7 +1170,7 @@ done:
 out_err:
 	free(buf);
 	perf_session__warn_about_errors(session, tool);
-	ordered_events__free(&session->ordered_events);
+	ordered_events__free(session, &session->ordered_events);
 	return err;
 }
 
@@ -1309,7 +1315,7 @@ out:
 out_err:
 	ui_progress__finish();
 	perf_session__warn_about_errors(session, tool);
-	ordered_events__free(&session->ordered_events);
+	ordered_events__free(session, &session->ordered_events);
 	session->one_mmap = false;
 	return err;
 }
diff --git a/tools/perf/util/session.h b/tools/perf/util/session.h
index 8dd41ca..137f77f 100644
--- a/tools/perf/util/session.h
+++ b/tools/perf/util/session.h
@@ -27,6 +27,7 @@ struct perf_session {
 	void			*one_mmap_addr;
 	u64			one_mmap_offset;
 	struct ordered_events	ordered_events;
+	bool			copy_on_queue;
 	struct perf_data_file	*file;
 };
 
-- 
1.9.1

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