linux-kernel - Re: [PATCH 2/5] perf tools: fix piped mode read code

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Date:	Mon, 14 May 2012 22:24:57 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	David Ahern <dsahern@...il.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	acme@...hat.com, namhyung.kim@....com
Subject: Re: [PATCH 2/5] perf tools: fix piped mode read code

On Fri, May 11, 2012 at 2:11 AM, David Ahern <dsahern@...il.com> wrote:
> Hi Stephane:
>
> This patch no longer applies cleanly. Can you update the series?
>
Will post the series again tomorrow.
Arnaldo, you need to take a look at this, it's been posted weeks ago.
We need this patch to make perf  in pipe mode behave like perf in
file mode.
Thanks
> David
>
>
> On 4/11/12 3:01 AM, Stephane Eranian wrote:
>>
>> In __perf_session__process_pipe_events(), there was a risk
>> we would read more than what a union perf_event struct can
>> hold. this could happen in case, perf is reading a file which
>> contains new record types it does not know about and which are
>> larger than anything it knows about.
>>
>> In general, perf is supposed to skip records it does not
>> understand, but in pipe mode, those have to be read and ignored.
>> The fixed size header contains the size of the record, but that
>> size may be larger than union perf_event, yet it was used as
>> the backing to the read in:
>>
>>   union perf_event event;
>>   void *p;
>>
>>   size = event->header.size;
>>
>>   p =&event;
>>   p += sizeof(struct perf_event_header);
>>   if (size - sizeof(struct perf_event_header)) {
>>     err = readn(self->fd, p, size - sizeof(struct perf_event_header));
>>
>> We fix this by allocating a buffer based on the size reported in
>> the header. We reuse the buffer as much as we can. We realloc in
>> case it becomes too small. In the  common case, the performance
>> impact is negligible.
>>
>> Signed-off-by: Stephane Eranian<eranian@...gle.com>
>> ---
>>  tools/perf/util/session.c |   35 +++++++++++++++++++++++++++--------
>>  1 files changed, 27 insertions(+), 8 deletions(-)
>>
>> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
>> index 9412e3b..d13e915 100644
>> --- a/tools/perf/util/session.c
>> +++ b/tools/perf/util/session.c
>> @@ -1056,8 +1056,9 @@ volatile int session_done;
>>  static int __perf_session__process_pipe_events(struct perf_session *self,
>>                                               struct perf_tool *tool)
>>  {
>> -       union perf_event event;
>> -       uint32_t size;
>> +       union perf_event *event;
>> +       uint32_t size, cur_size = 0;
>> +       void *buf = NULL;
>>        int skip = 0;
>>        u64 head;
>>        int err;
>> @@ -1066,8 +1067,14 @@ static int
>> __perf_session__process_pipe_events(struct perf_session *self,
>>        perf_tool__fill_defaults(tool);
>>
>>        head = 0;
>> +       cur_size = sizeof(union perf_event);
>> +
>> +       buf = malloc(cur_size);
>> +       if (!buf)
>> +               return -errno;
>>  more:
>> -       err = readn(self->fd,&event, sizeof(struct perf_event_header));
>>
>> +       event = buf;
>> +       err = readn(self->fd, event, sizeof(struct perf_event_header));
>>        if (err<= 0) {
>>                if (err == 0)
>>                        goto done;
>> @@ -1077,13 +1084,23 @@ static int
>> __perf_session__process_pipe_events(struct perf_session *self,
>>        }
>>
>>        if (self->header.needs_swap)
>> -               perf_event_header__bswap(&event.header);
>> +               perf_event_header__bswap(&event->header);
>>
>> -       size = event.header.size;
>> +       size = event->header.size;
>>        if (size == 0)
>>                size = 8;
>>
>> -       p =&event;
>> +       if (size>  cur_size) {
>> +               void *new = realloc(buf, size);
>> +               if (!new) {
>> +                       pr_err("failed to allocate memory to read
>> event\n");
>> +                       goto out_err;
>> +               }
>> +               buf = new;
>> +               cur_size = size;
>> +               event = buf;
>> +       }
>> +       p = event;
>>        p += sizeof(struct perf_event_header);
>>
>>        if (size - sizeof(struct perf_event_header)) {
>> @@ -1099,9 +1116,10 @@ static int
>> __perf_session__process_pipe_events(struct perf_session *self,
>>                }
>>        }
>>
>> -       if ((skip = perf_session__process_event(self,&event, tool, head))<
>>  0) {
>>
>> +       skip = perf_session__process_event(self, event, tool, head);
>> +       if (skip<  0) {
>>                dump_printf("%#" PRIx64 " [%#x]: skipping unknown header
>> type: %d\n",
>> -                           head, event.header.size, event.header.type);
>> +                           head, event->header.size, event->header.type);
>>                /*
>>                 * assume we lost track of the stream, check alignment, and
>>                 * increment a single u64 in the hope to catch on again
>> 'soon'.
>> @@ -1122,6 +1140,7 @@ static int
>> __perf_session__process_pipe_events(struct perf_session *self,
>>  done:
>>        err = 0;
>>  out_err:
>> +       free(buf);
>>        perf_session__warn_about_errors(self, tool);
>>        perf_session_free_sample_buffers(self);
>>        return err;
>
>
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