From 41ca1d1e88d485cb835a21032538e55102982a7a Mon Sep 17 00:00:00 2001 From: Ravi Bangoria Date: Tue, 25 May 2021 10:07:44 +0530 Subject: [PATCH] perf probe: Provide more detail with relocation warning 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. Reported-by: Aneesh Kumar K.V Signed-off-by: Ravi Bangoria Acked-by: Masami Hiramatsu Cc: Jiri Olsa Link: http://lore.kernel.org/lkml/20210525043744.193297-1-ravi.bangoria@linux.ibm.com Signed-off-by: Arnaldo Carvalho de Melo --- 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; }