Messages in this thread | | | Date | Tue, 25 May 2021 21:48:58 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH] perf probe: Provide more detail with relocation warning |
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On Tue, 25 May 2021 10:07:44 +0530 Ravi Bangoria <ravi.bangoria@linux.ibm.com> wrote:
> When run as normal user with default sysctl kernel.kptr_restrict=0 > and kernel.perf_event_paranoid=2, perf probe fails with: > > $ ./perf probe move_page_tables > Relocated base symbol is not found! > > The warning message is not much informative. The reason perf fails > is because /proc/kallsyms is restricted by perf_event_paranoid=2 > for normal user and thus perf fails to read relocated address of > the base symbol. > > Tweaking kptr_restrict and perf_event_paranoid can change the > behavior of perf probe. Also, running as root or privileged user > works too. Add these details in the warning message. > > Plus, kmap->ref_reloc_sym might not be always set even if > host_machine is initialized. Above is the example of the same. > Remove that comment.
Yes, those are restricted in some cases. Anyway without priviledged (super) user, perf probe can not set the probe in ftrace.
Hmm, I think it should check the effective user-id at first. If it is not super user and the action will access tracefs and kallsyms, it should warn at that point.
Thank you,
> > Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> > Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com> > --- > tools/perf/util/probe-event.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c > index a78c8d59a555..3a7649835ec9 100644 > --- a/tools/perf/util/probe-event.c > +++ b/tools/perf/util/probe-event.c > @@ -108,7 +108,6 @@ void exit_probe_symbol_maps(void) > > static struct ref_reloc_sym *kernel_get_ref_reloc_sym(struct map **pmap) > { > - /* kmap->ref_reloc_sym should be set if host_machine is initialized */ > struct kmap *kmap; > struct map *map = machine__kernel_map(host_machine); > > @@ -819,7 +818,10 @@ post_process_kernel_probe_trace_events(struct probe_trace_event *tevs, > > reloc_sym = kernel_get_ref_reloc_sym(&map); > if (!reloc_sym) { > - pr_warning("Relocated base symbol is not found!\n"); > + pr_warning("Relocated base symbol is not found! " > + "Check /proc/sys/kernel/kptr_restrict\n" > + "and /proc/sys/kernel/perf_event_paranoid. " > + "Or run as privileged perf user.\n\n"); > return -EINVAL; > } > > @@ -3025,7 +3027,10 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev, > (!pp->retprobe || kretprobe_offset_is_supported())) { > reloc_sym = kernel_get_ref_reloc_sym(NULL); > if (!reloc_sym) { > - pr_warning("Relocated base symbol is not found!\n"); > + pr_warning("Relocated base symbol is not found! " > + "Check /proc/sys/kernel/kptr_restrict\n" > + "and /proc/sys/kernel/perf_event_paranoid. " > + "Or run as privileged perf user.\n\n"); > ret = -EINVAL; > goto out; > } > -- > 2.31.1 >
-- Masami Hiramatsu <mhiramat@kernel.org>
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