linux-kernel - Re: [PATCH] perf/core: restore mmap record type correctly

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Message-ID: <20190307190330.GA2443@redhat.com>
Date:   Thu, 7 Mar 2019 16:03:30 -0300
From:   Arnaldo Carvalho de Melo <acme@...hat.com>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, peterz@...radead.org, mingo@...e.hu,
        jolsa@...hat.com, acme@...nel.org
Subject: Re: [PATCH] perf/core: restore mmap record type correctly

Em Thu, Mar 07, 2019 at 10:52:33AM -0800, Stephane Eranian escreveu:
> On mmap(), perf_events generates a RECORD_MMAP record and then checks
> which events are interested in this record. There are currently 2 versions
> of mmap records: RECORD_MMAP and RECORD_MMAP2. MMAP2 is larger. The event
> configuration controls which version the user level tool accepts. If the
> event->attr.mmap2=1 field then MMAP2 record is returned. The
> perf_event_mmap_output() takes care of this. It checks attr->mmap2 and corrects
> the record fields before putting it in the sampling buffer of the event.
> At the end the function restores the modified MMAP record fields.
> 
> The problem is that the function restores the size but not the
> type. Thus, if a subsequent event only accepts MMAP type, then it would
> instead receive an MMAP2 record with a size of MMAP record.
> 
> This patch fixes the problem by restoring the record type on exit.

Right, simple enough, bug fixed, Peter, I'm taking this one, ok?

- Arnaldo
 
> Signed-off-by: Stephane Eranian <eranian@...gle.com>
> ---
>  kernel/events/core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 5f59d848171e..f170cd12beed 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7188,6 +7188,7 @@ static void perf_event_mmap_output(struct perf_event *event,
>  	struct perf_output_handle handle;
>  	struct perf_sample_data sample;
>  	int size = mmap_event->event_id.header.size;
> +	u32 type = mmap_event->event_id.header.type;
>  	int ret;
>  
>  	if (!perf_event_mmap_match(event, data))
> @@ -7231,6 +7232,7 @@ static void perf_event_mmap_output(struct perf_event *event,
>  	perf_output_end(&handle);
>  out:
>  	mmap_event->event_id.header.size = size;
> +	mmap_event->event_id.header.type = type;
>  }
>  
>  static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
> -- 
> 2.21.0.360.g471c308f928-goog