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Date:   Tue, 22 Sep 2020 12:50:35 -0700
From:   Andi Kleen <ak@linux.intel.com>
To:     Wei Li <liwei391@huawei.com>
Cc:     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>,
        Alexey Budankov <alexey.budankov@linux.intel.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, huawei.libin@huawei.com
Subject: Re: [PATCH 1/2] perf stat: Fix segfault when counting armv8_pmu
 events
Message-ID: <20200922195035.GA42577@tassilo.jf.intel.com>
References: <20200922031346.15051-1-liwei391@huawei.com>
 <20200922031346.15051-2-liwei391@huawei.com>
 <20200922192321.GL13818@tassilo.jf.intel.com>
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On Tue, Sep 22, 2020 at 12:23:21PM -0700, Andi Kleen wrote:
> > After debugging, i found the root reason is that the xyarray fd is created
> > by evsel__open_per_thread() ignoring the cpu passed in
> > create_perf_stat_counter(), while the evsel' cpumap is assigned as the
> > corresponding PMU's cpumap in __add_event(). Thus, the xyarray fd is created
> > with ncpus of dummy cpumap and an out of bounds 'cpu' index will be used in
> > perf_evsel__close_fd_cpu().
> > 
> > To address this, add a flag to mark this situation and avoid using the
> > affinity technique when closing/enabling/disabling events.
> 
> The flag seems like a hack. How about figuring out the correct number of 
> CPUs and using that?

Also would like to understand what's different on ARM64 than other architectures.
Or could this happen on x86 too?

-Andi