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Date:   Fri, 7 Aug 2020 09:08:24 -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: <20200807120824.GA2456573@kernel.org>
References: <20200805022937.29184-1-yao.jin@linux.intel.com>
 <20200806194357.GA539212@krava>
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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.

Applied,

- Arnaldo
 
> thanks,
> jirka
> 
> > 
> > The root cause is, evlist__add_bpf_sb_event() just returns 0 if
> > HAVE_LIBBPF_SUPPORT is not defined (inline function path). So it will
> > not create a valid evsel for side-band event.
> > 
> > But perf-record still creates BPF side band thread to process the
> > side-band event, then the error happpens.
> > 
> > We can reproduce this issue by removing the libelf-dev. e.g.
> > 1. apt-get remove libelf-dev
> > 2. perf record -a -- sleep 1
> > 
> > root@test:~# ./perf record -a -- sleep 1
> > perf: Segmentation fault
> > Obtained 6 stack frames.
> > ./perf(+0x28eee8) [0x5562d6ef6ee8]
> > /lib/x86_64-linux-gnu/libc.so.6(+0x46210) [0x7fbfdc65f210]
> > ./perf(+0x342e74) [0x5562d6faae74]
> > ./perf(+0x257e39) [0x5562d6ebfe39]
> > /lib/x86_64-linux-gnu/libpthread.so.0(+0x9609) [0x7fbfdc990609]
> > /lib/x86_64-linux-gnu/libc.so.6(clone+0x43) [0x7fbfdc73b103]
> > Segmentation fault (core dumped)
> > 
> > To fix this issue,
> > 
> > 1. We either install the missing libraries to let HAVE_LIBBPF_SUPPORT
> >    be defined.
> >    e.g. apt-get install libelf-dev and install other related libraries.
> > 
> > 2. Use this patch to skip the side-band event setup if HAVE_LIBBPF_SUPPORT
> >    is not set.
> > 
> > Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
> > ---
> >  tools/perf/builtin-record.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> > index b6bdccd875bc..ae97f98e2753 100644
> > --- a/tools/perf/builtin-record.c
> > +++ b/tools/perf/builtin-record.c
> > @@ -1506,6 +1506,7 @@ static int record__synthesize(struct record *rec, bool tail)
> >  	return err;
> >  }
> >  
> > +#ifdef HAVE_LIBBPF_SUPPORT
> >  static int record__process_signal_event(union perf_event *event __maybe_unused, void *data)
> >  {
> >  	struct record *rec = data;
> > @@ -1550,6 +1551,12 @@ static int record__setup_sb_evlist(struct record *rec)
> >  
> >  	return 0;
> >  }
> > +#else
> > +static int record__setup_sb_evlist(struct record *rec __maybe_unused)
> > +{
> > +	return 0;
> > +}
> > +#endif
> >  
> >  static int __cmd_record(struct record *rec, int argc, const char **argv)
> >  {
> > -- 
> > 2.17.1
> > 
> 

-- 

- Arnaldo