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Date:   Fri, 7 Aug 2020 09:09:56 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Jiri Olsa <jolsa@redhat.com>
Cc:     Jin Yao <yao.jin@linux.intel.com>, jolsa@kernel.org,
        peterz@infradead.org, mingo@redhat.com,
        alexander.shishkin@linux.intel.com, Linux-kernel@vger.kernel.org,
        ak@linux.intel.com, kan.liang@intel.com, yao.jin@intel.com
Subject: Re: [PATCH] perf record: Skip side-band event setup if
 HAVE_LIBBPF_SUPPORT is not set
Message-ID: <20200807120956.GB2456573@kernel.org>
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 <20200807120824.GA2456573@kernel.org>
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Em Fri, Aug 07, 2020 at 09:08:24AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Thu, Aug 06, 2020 at 09:43:57PM +0200, Jiri Olsa escreveu:
> > On Wed, Aug 05, 2020 at 10:29:37AM +0800, Jin Yao wrote:
> > > We received an error report that perf-record caused 'Segmentation fault'
> > > on a newly system (e.g. on the new installed ubuntu).
> > > 
> > >  (gdb) backtrace
> > >  #0  __read_once_size (size=4, res=<synthetic pointer>, p=0x14) at /root/0-jinyao/acme/tools/include/linux/compiler.h:139
> > >  #1  atomic_read (v=0x14) at /root/0-jinyao/acme/tools/include/asm/../../arch/x86/include/asm/atomic.h:28
> > >  #2  refcount_read (r=0x14) at /root/0-jinyao/acme/tools/include/linux/refcount.h:65
> > >  #3  perf_mmap__read_init (map=map@entry=0x0) at mmap.c:177
> > >  #4  0x0000561ce5c0de39 in perf_evlist__poll_thread (arg=0x561ce68584d0) at util/sideband_evlist.c:62
> > >  #5  0x00007fad78491609 in start_thread (arg=<optimized out>) at pthread_create.c:477
> > >  #6  0x00007fad7823c103 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
> > 
> > hum, I recall discussing the same issue,
> > I thought it was already fixed :-\ in any case:
> > 
> > Acked-by: Jiri Olsa <jolsa@redhat.com>
> 
> I added this:
> 
> Fixes: 23cbb41c939a ("perf record: Move side band evlist setup to separate routine")
> 
> To help this fixe go back to a few stable kernels. Technically the
> problem was introduced much earlier, when the side band thread was
> added, but then this would require more cherry-picking of patches and
> since we have a workaround, i.e. build with libbpf, I think this is
> enough.

I backtrack on that, as the sideband event is not just for BPF... The
switch-output-event code uses it as well, so it can't be dependent on
LIBBPF being built...

I'll see what I can do

- Arnaldo