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Date:   Thu, 26 Nov 2020 13:13:29 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Stephane Eranian <eranian@...gle.com>,
        John Sperbeck <jsperbeck@...gle.com>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [PATCH 1/2] perf/x86/intel: Fix a warning on x86_pmu_stop() with
 large PEBS

On Thu, Nov 26, 2020 at 08:09:21PM +0900, Namhyung Kim wrote:
> The commit 3966c3feca3f ("x86/perf/amd: Remove need to check "running"
> bit in NMI handler") introduced this.  It seems x86_pmu_stop can be
> called recursively (like when it losts some samples) like below:
> 
>   x86_pmu_stop
>     intel_pmu_disable_event  (x86_pmu_disable)
>       intel_pmu_pebs_disable
>         intel_pmu_drain_pebs_nhm  (x86_pmu_drain_pebs_buffer)
>           x86_pmu_stop
> 
> While commit 35d1ce6bec13 ("perf/x86/intel/ds: Fix x86_pmu_stop
> warning for large PEBS") fixed it for the normal cases, there's
> another path to call x86_pmu_stop() recursively when a PEBS error was
> detected (like two or more counters overflowed at the same time).
> 
> Like in the Kan's previous fix, we can skip the interrupt accounting
> for large PEBS, so check the iregs which is set for PMI only.
> 
> Fixes: 3966c3feca3f ("x86/perf/amd: Remove need to check "running" bit in NMI handler")
> Reported-by: John Sperbeck <jsperbeck@...gle.com>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Cc: "Lendacky, Thomas" <Thomas.Lendacky@....com>
> Cc: Kan Liang <kan.liang@...ux.intel.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

Thanks for both!

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