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

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Date:   Wed, 23 Sep 2020 16:07:47 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Wei Li <liwei391@...wei.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        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 <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Li Bin <huawei.libin@...wei.com>
Subject: Re: [PATCH 1/2] perf stat: Fix segfault when counting armv8_pmu
 events

On Wed, Sep 23, 2020 at 10:49:52PM +0900, Namhyung Kim wrote:
> On Wed, Sep 23, 2020 at 2:44 PM Jiri Olsa <jolsa@...hat.com> wrote:
> >
> > On Tue, Sep 22, 2020 at 11:13:45AM +0800, Wei Li wrote:
> > > When executing perf stat with armv8_pmu events with a workload, it will
> > > report a segfault as result.
> >
> > please share the perf stat command line you see that segfault for
> 
> It seems the description in the patch 0/2 already has it:
> 
>   [root@...alhost hulk]# tools/perf/perf stat  -e
> armv8_pmuv3_0/ll_cache_rd/,armv8_pmuv3_0/ll_cache_miss_rd/ ls >
> /dev/null
>   Segmentation fault

yea I found it, but can't reproduce it.. I see the issue from
patch 2, but not sure what's the problem so far

jirka

> 
> Thanks
> Namhyun
> 
> 
> >
> > thanks,
> > jirka
> >
> > >
> > > (gdb) bt
> > > #0  0x0000000000603fc8 in perf_evsel__close_fd_cpu (evsel=<optimized out>,
> > >     cpu=<optimized out>) at evsel.c:122
> > > #1  perf_evsel__close_cpu (evsel=evsel@...ry=0x716e950, cpu=7) at evsel.c:156
> > > #2  0x00000000004d4718 in evlist__close (evlist=0x70a7cb0) at util/evlist.c:1242
> > > #3  0x0000000000453404 in __run_perf_stat (argc=3, argc@...ry=1, argv=0x30,
> > >     argv@...ry=0xfffffaea2f90, run_idx=119, run_idx@...ry=1701998435)
> > >     at builtin-stat.c:929
> > > #4  0x0000000000455058 in run_perf_stat (run_idx=1701998435, argv=0xfffffaea2f90,
> > >     argc=1) at builtin-stat.c:947
> > > #5  cmd_stat (argc=1, argv=0xfffffaea2f90) at builtin-stat.c:2357
> > > #6  0x00000000004bb888 in run_builtin (p=p@...ry=0x9764b8 <commands+288>,
> > >     argc=argc@...ry=4, argv=argv@...ry=0xfffffaea2f90) at perf.c:312
> > > #7  0x00000000004bbb54 in handle_internal_command (argc=argc@...ry=4,
> > >     argv=argv@...ry=0xfffffaea2f90) at perf.c:364
> > > #8  0x0000000000435378 in run_argv (argcp=<synthetic pointer>,
> > >     argv=<synthetic pointer>) at perf.c:408
> > > #9  main (argc=4, argv=0xfffffaea2f90) at perf.c:538
> > >
> > > 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.
> > >
> > > Fixes: 7736627b865d ("perf stat: Use affinity for closing file descriptors")
> > > Fixes: 704e2f5b700d ("perf stat: Use affinity for enabling/disabling events")
> > > Signed-off-by: Wei Li <liwei391@...wei.com>
> > > ---
>