linux-kernel - Re: [PATCH 1/2] perf stat: Fix segfault when counting armv8

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Message-ID: <20200922195035.GA42577@tassilo.jf.intel.com>
Date:   Tue, 22 Sep 2020 12:50:35 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Wei Li <liwei391@...wei.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, huawei.libin@...wei.com
Subject: Re: [PATCH 1/2] perf stat: Fix segfault when counting armv8_pmu
 events

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