linux-kernel - Re: [PATCH v2] perf tools: perf_event_paranoid and kptr

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Date:   Fri, 26 Feb 2021 08:54:19 +0800
From:   JackieLiu <jackieliu2113@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Jackie Liu <liuyun01@...inos.cn>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v2] perf tools: perf_event_paranoid and kptr_restrict may
 crash on 'perf top'

Thanks jirka, I will check again, and I saw another crash after this
patch, so I  need to debug again.

BR, Jackie Liu

Jiri Olsa <jolsa@...hat.com> 于2021年2月26日周五 上午12:11写道：
>
> On Thu, Feb 25, 2021 at 02:25:30PM +0800, Jackie Liu wrote:
> > After install the libelf-dev package and compiling perf, kptr_restrict=2
> > and perf_event_paranoid=3 will cause perf top to crash, because the
> > value of /proc/kallsyms cannot be obtained, which leads to
> > info->jited_ksyms == NULL. In order to solve this problem, Add a
> > judgment before use.
> >
> > Suggested-by: Jiri Olsa <jolsa@...hat.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Signed-off-by: Jackie Liu <liuyun01@...inos.cn>
> > ---
> >  tools/perf/util/bpf-event.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/tools/perf/util/bpf-event.c b/tools/perf/util/bpf-event.c
> > index 57d58c81a5f8..b1ce2d189d37 100644
> > --- a/tools/perf/util/bpf-event.c
> > +++ b/tools/perf/util/bpf-event.c
> > @@ -225,6 +225,11 @@ static int perf_event__synthesize_one_bpf_prog(struct perf_session *session,
> >               perf_env__fetch_btf(env, info->btf_id, btf);
> >       }
> >
> > +     if (!info->jited_ksyms) {
> > +             err = -1;
> > +             goto out;
> > +     }
> > +
>
> I think this check should be moved above, right after line:
>
>         info = &info_linear->info;
>
> so we don't do those extra btf checks
>
> thanks,
> jirka
>
> >       /* Synthesize PERF_RECORD_KSYMBOL */
> >       for (i = 0; i < sub_prog_cnt; i++) {
> >               __u32 *prog_lens = (__u32 *)(uintptr_t)(info->jited_func_lens);
> > --
> > 2.25.1
> >
>