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    SubjectRe: [PATCH] perf record: Skip side-band event setup if HAVE_LIBBPF_SUPPORT is not set
    Em Fri, Aug 07, 2020 at 09:09:56AM -0300, Arnaldo Carvalho de Melo escreveu:
    > 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

    So this is the change I made, the side band thread is may have been
    already created by

    [acme@quaco ~]$ perf record -h switch-output-event

    Usage: perf record [<options>] [<command>]
    or: perf record [<options>] -- <command> [<options>]

    --switch-output-event <switch output event>
    switch output event selector. use 'perf list' to list available events

    [acme@quaco ~]$

    I'm doing some extra checking now on your report, and the patch below
    has skews because it clashed with the clockid patches by Jiri so I had
    to resolve its merge.

    diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
    index 7d97c8e9f7f9..c12b5b072519 100644
    --- a/tools/perf/builtin-record.c
    +++ b/tools/perf/builtin-record.c
    @@ -1511,6 +1511,7 @@ 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;
    @@ -1592,6 +1593,12 @@ static int record__init_clock(struct record *rec)
    session->header.env.clock.clockid_ns = ref;
    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)
    {
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