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

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Date:   Tue, 11 Apr 2017 11:40:50 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     David Carrillo-Cisneros <davidcc@...gle.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Simon Que <sque@...omium.org>,
        Wang Nan <wangnan0@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
        He Kuang <hekuang@...wei.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH 2/7] perf inject: copy events when reordering events in
 pipe mode

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@...gle.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
>