linux-kernel - Re: [RFC] perf/x86: Fix a warning on x86_pmu

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Message-ID: <CAM9d7chpprnGZEOrTGYE1j1+HyCnr6tYC+Upjh06X5JiLp8-UQ@mail.gmail.com>
Date:   Wed, 25 Nov 2020 16:22:09 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        John Sperbeck <jsperbeck@...gle.com>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>
Subject: Re: [RFC] perf/x86: Fix a warning on x86_pmu_stop()

On Tue, Nov 24, 2020 at 5:10 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Nov 24, 2020 at 02:01:39PM +0900, Namhyung Kim wrote:
>
> > Yes, it's not about __intel_pmu_pebs_event().  I'm looking at
> > intel_pmu_drain_pebs_nhm() specifically.  There's code like
> >
> >         /* log dropped samples number */
> >         if (error[bit]) {
> >             perf_log_lost_samples(event, error[bit]);
> >
> >             if (perf_event_account_interrupt(event))
> >                 x86_pmu_stop(event, 0);
> >         }
> >
> >         if (counts[bit]) {
> >             __intel_pmu_pebs_event(event, iregs, base,
> >                            top, bit, counts[bit],
> >                            setup_pebs_fixed_sample_data);
> >         }
> >
> > There's a path to x86_pmu_stop() when an error bit is on.
>
> That would seem to suggest you try something like this:
>
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index 31b9e58b03fe..8c6ee8be8b6e 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -1945,7 +1945,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_d
>                 if (error[bit]) {
>                         perf_log_lost_samples(event, error[bit]);
>
> -                       if (perf_event_account_interrupt(event))
> +                       if (iregs && perf_event_account_interrupt(event))
>                                 x86_pmu_stop(event, 0);
>                 }
>

That would work too and much simpler!

Thanks,
Namhyung