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

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Message-ID: <20190307190939.GB2482@worktop.programming.kicks-ass.net>
Date:   Thu, 7 Mar 2019 20:09:39 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:     Stephane Eranian <eranian@...gle.com>,
        linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, mingo@...e.hu, jolsa@...hat.com,
        acme@...nel.org
Subject: Re: [PATCH] perf/core: restore mmap record type correctly

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>