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 11:56:22 -0700
From:   David Carrillo-Cisneros <davidcc@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     linux-kernel <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

free_dup_event is called in two places
  1) ordered_events__free
  2) ordered_events__delete

without this patch, calling 1) after 2) would cause a double
de-allocation, but that's exactly what happens in
__perf_session__process_pipe_events. It wasn't triggered before
because events where not copied when queued.

With this patch, the event->event = NULL in ordered_events__delete
will clear event pointer that is checked in free_dup_event, avoiding
de-allocating the event a second time.

Thanks,
David

On Tue, Apr 11, 2017 at 2:40 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> 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
>>