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

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Message-ID: <20190307192639.GC32240@kernel.org>
Date:   Thu, 7 Mar 2019 16:26:39 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf/core: restore mmap record type correctly

Em Thu, Mar 07, 2019 at 08:09:39PM +0100, Peter Zijlstra escreveu:
> On Thu, Mar 07, 2019 at 04:03:30PM -0300, Arnaldo Carvalho de Melo wrote:
> > 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?
 
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

BTW, added:

    Fixes: 13d7a2410fa6 ("perf: Add attr->mmap2 attribute to an event")

For the stable guys to pick this up. Please try to add the fixes tag in
the future.

Thanks,

- Arnaldo