linux-kernel - Re: [PATCH v4 3/3] perf/core: Check sample_type in perf_sample_save

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Date: Wed, 15 May 2024 10:47:11 -0700
From: Yabin Cui <yabinc@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Namhyung Kim <namhyung@...nel.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	bpf@...r.kernel.org
Subject: Re: [PATCH v4 3/3] perf/core: Check sample_type in perf_sample_save_brstack

On Wed, May 15, 2024 at 1:58 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, May 10, 2024 at 02:29:58PM -0700, Namhyung Kim wrote:
> > On Fri, May 10, 2024 at 12:14 PM Yabin Cui <yabinc@...gle.com> wrote:
> > >
> > > Check sample_type in perf_sample_save_brstack() to prevent
> > > saving branch stack data when it isn't required.
> > >
> > > Suggested-by: Namhyung Kim <namhyung@...nel.org>
> > > Signed-off-by: Yabin Cui <yabinc@...gle.com>
> >
> > It seems powerpc has the similar bug, then you need this:
> >
> > Fixes: eb55b455ef9c ("perf/core: Add perf_sample_save_brstack() helper")
>
> Is this really a bug? AFAICT it just does unneeded work, no?

It's not a bug. As I replied to Namhyuang, the powerpc code checks
sample_type before calling perf_sample_save_brstack().