Re: [PATCH 2/7] perf inject: copy events when reordering events in pipe mode

Jiri Olsa
2017-04-11T09:40:57Z

On Mon, Apr 10, 2017 at 01:14:27PM -0700, David Carrillo-Cisneros wrote:
> __perf_session__process_pipe_events reuses the same memory buffer to
> process all events in the pipe.
>
> When reordering is needed (e.g. -b option), events are not immediately
> flushed, but kept around until reordering is possible, causing
> memory corruption.
>
> The problem is usually observed by a "Unknown sample error" output. It
> can easily be reproduced by:
>
> perf record -o - noploop | perf inject -b > output
>
> Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
> ---
> tools/perf/util/ordered-events.c | 3 ++-
> tools/perf/util/session.c | 1 +
> 2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/ordered-events.c b/tools/perf/util/ordered-events.c
> index fe84df1875aa..e70e935b1841 100644
> --- a/tools/perf/util/ordered-events.c
> +++ b/tools/perf/util/ordered-events.c
> @@ -79,7 +79,7 @@ static union perf_event *dup_event(struct ordered_events *oe,
>
> static void free_dup_event(struct ordered_events *oe, union perf_event *event)
> {
> - if (oe->copy_on_queue) {
> + if (event && oe->copy_on_queue) {
> oe->cur_alloc_size -= event->header.size;
> free(event);
> }
> @@ -150,6 +150,7 @@ void ordered_events__delete(struct ordered_events *oe, struct ordered_event *eve
> list_move(&event->list, &oe->cache);
> oe->nr_events--;
> free_dup_event(oe, event->event);
> + event->event = NULL;

based on the changelog I understand the need for the change below,
but I dont get why do we need this cleanu and check above

thanks,
jirka

> }
>
> int ordered_events__queue(struct ordered_events *oe, union perf_event *event,
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index 24259bc2c598..a25302bc55a8 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1656,6 +1656,7 @@ static int __perf_session__process_pipe_events(struct perf_session *session)
> buf = malloc(cur_size);
> if (!buf)
> return -errno;
> + ordered_events__set_copy_on_queue(oe, true);
> more:
> event = buf;
> err = readn(fd, event, sizeof(struct perf_event_header));
> --
> 2.12.2.715.g7642488e1d-goog
>