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Date:   Mon, 10 Aug 2020 08:35:00 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, jolsa@...nel.org,
        peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH] perf record: Skip side-band event setup if
 HAVE_LIBBPF_SUPPORT is not set

Hi Arnaldo,

On 8/7/2020 8:28 PM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Aug 07, 2020 at 09:16:29AM -0300, Arnaldo Carvalho de Melo escreveu:
>> 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@...ry=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@...hat.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@...co ~]$ 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@...co ~]$
>>
>> 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.
>   
> Sorry, I resent your patch, doh, here is the end result, with my change,
> its ok to call perf_evlist__start_sb_thread() with a NULL evlist, it'll
> just return 0.
> 
> - Arnald
> 
> 
> commit b13536a7e93680625094beb18cdce4ae47a3dbfb
> Author: Jin Yao <yao.jin@...ux.intel.com>
> Date:   Wed Aug 5 10:29:37 2020 +0800
> 
>      perf record: Skip side-band event setup if HAVE_LIBBPF_SUPPORT is not set
>      
>      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@...ry=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
>      
>      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@...t:~# ./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.
>      
>      Committer notes:
>      
>      The side band thread is not used just with BPF, it is also used with
>      --switch-output-event, so narrow the ifdef to the BPF specific part.
>      
>      Fixes: 23cbb41c939a ("perf record: Move side band evlist setup to separate routine")
>      Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>
>      Acked-by: Jiri Olsa <jolsa@...nel.org>
>      Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
>      Cc: Andi Kleen <ak@...ux.intel.com>
>      Cc: Jin Yao <yao.jin@...el.com>
>      Cc: Kan Liang <kan.liang@...ux.intel.com>
>      Cc: Peter Zijlstra <peterz@...radead.org>
>      Link: http://lore.kernel.org/lkml/20200805022937.29184-1-yao.jin@linux.intel.com
>      Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 7d97c8e9f7f9..f91352f847c0 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1531,7 +1531,7 @@ static int record__setup_sb_evlist(struct record *rec)
>   		evlist__set_cb(rec->sb_evlist, record__process_signal_event, rec);
>   		rec->thread_id = pthread_self();
>   	}
> -
> +#ifdef HAVE_LIBBPF_SUPPORT
>   	if (!opts->no_bpf_event) {
>   		if (rec->sb_evlist == NULL) {
>   			rec->sb_evlist = evlist__new();
> @@ -1547,7 +1547,7 @@ static int record__setup_sb_evlist(struct record *rec)
>   			return -1;
>   		}
>   	}
> -
> +#endif
>   	if (perf_evlist__start_sb_thread(rec->sb_evlist, &rec->opts.target)) {
>   		pr_debug("Couldn't start the BPF side band thread:\nBPF programs starting from now on won't be annotatable\n");
>   		opts->no_bpf_event = true;
> 

Thanks so much for helping to refine the patch!

Thanks
Jin Yao

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