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From:   Vince Weaver <vincent.weaver@maine.edu>
Date:   Tue, 2 Mar 2021 00:29:44 -0500 (EST)
To:     "Liang, Kan" <kan.liang@linux.intel.com>
cc:     Peter Zijlstra <peterz@infradead.org>,
        Vince Weaver <vincent.weaver@maine.edu>,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Stephane Eranian <eranian@google.com>
Subject: Re: [perf] perf_fuzzer causes crash in intel_pmu_drain_pebs_nhm()
In-Reply-To: <32888c33-c286-c600-66cb-8b1b03beeb8b@linux.intel.com>
Message-ID: <ae72b937-6a1b-cf61-353f-eeec9dfb8557@maine.edu>
References: <61a56699-aab4-ef6-ed8d-a22b6bf532d@maine.edu> <7170d3b-c17f-1ded-52aa-cc6d9ae999f4@maine.edu> <YCVE8q4MlbcU4fnV@hirez.programming.kicks-ass.net> <32888c33-c286-c600-66cb-8b1b03beeb8b@linux.intel.com>
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On Mon, 1 Mar 2021, Liang, Kan wrote:

> https://lore.kernel.org/lkml/tip-01330d7288e0050c5aaabc558059ff91589e67cd@git.kernel.org/
> The patch is an SW workaround for some old CPUs (HSW and earlier), which may
> set 0 to the PEBS status. It adds a check in the intel_pmu_drain_pebs_nhm().
> It tries to minimize the impact of the defect by avoiding dropping the PEBS
> records which have PEBS status 0.
> But, it doesn't correct the PEBS status, which may bring problems,
> especially for the large PEBS.
> It's possible that all the PEBS records in a large PEBS have the PEBS status
> 0. If so, the first get_next_pebs_record_by_bit() in the
> __intel_pmu_pebs_event() returns NULL. The at = NULL. Since it's a large PEBS,
> the 'count' parameter must > 1. The second get_next_pebs_record_by_bit() will
> crash.
> 
> Could you please revert the patch and check whether it fixes your issue?

I've reverted that patch and my test-case no longer triggers the issue.

I'll restart a longer fuzzing run to see if any other issues turn up.

Thanks,

Vince