Re: [PATCH] perf record: Skip side-band event setup if HAVE_LIBBPF_SUPPORT is not set

[Jiri Olsa]

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@xxxxxxxxxx>

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@xxxxxxxxxxxxxxx>
> ---
>  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
>