linux-kernel - Re: [Patch v3 3/7] perf/x86: Check if cpuc->events[*] pointer exists before accessing it

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Message-ID: <aKVD4ATXW4LmhDJm@tassilo>
Date: Tue, 19 Aug 2025 20:41:20 -0700
From: Andi Kleen <ak@...ux.intel.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Eranian Stephane <eranian@...gle.com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org, Dapeng Mi <dapeng1.mi@...el.com>,
	kernel test robot <oliver.sang@...el.com>
Subject: Re: [Patch v3 3/7] perf/x86: Check if cpuc->events[*] pointer exists
 before accessing it

>  		event = cpuc->events[bit];
> +		/*
> +		 * perf_event_overflow() called by below __intel_pmu_pebs_last_event()
> +		 * could trigger interrupt throttle and clear all event pointers of the
> +		 * group in cpuc->events[] to NULL. So need to re-check if cpuc->events[*]
> +		 * is NULL, if so it indicates the event has been throttled (stopped) and
> +		 * the corresponding last PEBS records have been processed in stopping
> +		 * event, don't need to process it again.
> +		 */
> +		if (!event)
> +			continue;

Then we silently ignore the overflow. Would be better to log at least an overflow
packet or something like that.

-Andi