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

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Message-ID: <20201124080951.GE2414@hirez.programming.kicks-ass.net>
Date:   Tue, 24 Nov 2020 09:09:51 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Namhyung Kim <namhyung@...nel.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 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);
 		}