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Message-ID: <CAP-5=fU+8OdM+9jH_dKPiZJqyTJUdQcS-Hh3ynoYwocRw2RDLw@mail.gmail.com>
Date: Wed, 14 May 2025 08:06:07 -0700
From: Ian Rogers <irogers@...gle.com>
To: Thomas Falcon <thomas.falcon@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>,
linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 2/2 v3] perf top: populate PMU capabilities data in perf_env
On Tue, May 13, 2025 at 4:18 PM Thomas Falcon <thomas.falcon@...el.com> wrote:
>
> Calling perf top with branch filters enabled on Intel CPU's
> with branch counters logging (A.K.A LBR event logging [1]) support
> results in a segfault.
>
> Thread 27 "perf" received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0x7fffafff76c0 (LWP 949003)]
> perf_env__find_br_cntr_info (env=0xf66dc0 <perf_env>, nr=0x0, width=0x7fffafff62c0) at util/env.c:653
> 653 *width = env->cpu_pmu_caps ? env->br_cntr_width :
> (gdb) bt
> #0 perf_env__find_br_cntr_info (env=0xf66dc0 <perf_env>, nr=0x0, width=0x7fffafff62c0) at util/env.c:653
> #1 0x00000000005b1599 in symbol__account_br_cntr (branch=0x7fffcc3db580, evsel=0xfea2d0, offset=12, br_cntr=8) at util/annotate.c:345
> #2 0x00000000005b17fb in symbol__account_cycles (addr=5658172, start=5658160, sym=0x7fffcc0ee420, cycles=539, evsel=0xfea2d0, br_cntr=8) at util/annotate.c:389
> #3 0x00000000005b1976 in addr_map_symbol__account_cycles (ams=0x7fffcd7b01d0, start=0x7fffcd7b02b0, cycles=539, evsel=0xfea2d0, br_cntr=8) at util/annotate.c:422
> #4 0x000000000068d57f in hist__account_cycles (bs=0x110d288, al=0x7fffafff6540, sample=0x7fffafff6760, nonany_branch_mode=false, total_cycles=0x0, evsel=0xfea2d0) at util/hist.c:2850
> #5 0x0000000000446216 in hist_iter__top_callback (iter=0x7fffafff6590, al=0x7fffafff6540, single=true, arg=0x7fffffff9e00) at builtin-top.c:737
> #6 0x0000000000689787 in hist_entry_iter__add (iter=0x7fffafff6590, al=0x7fffafff6540, max_stack_depth=127, arg=0x7fffffff9e00) at util/hist.c:1359
> #7 0x0000000000446710 in perf_event__process_sample (tool=0x7fffffff9e00, event=0x110d250, evsel=0xfea2d0, sample=0x7fffafff6760, machine=0x108c968) at builtin-top.c:845
> #8 0x0000000000447735 in deliver_event (qe=0x7fffffffa120, qevent=0x10fc200) at builtin-top.c:1211
> #9 0x000000000064ccae in do_flush (oe=0x7fffffffa120, show_progress=false) at util/ordered-events.c:245
> #10 0x000000000064d005 in __ordered_events__flush (oe=0x7fffffffa120, how=OE_FLUSH__TOP, timestamp=0) at util/ordered-events.c:324
> #11 0x000000000064d0ef in ordered_events__flush (oe=0x7fffffffa120, how=OE_FLUSH__TOP) at util/ordered-events.c:342
> #12 0x00000000004472a9 in process_thread (arg=0x7fffffff9e00) at builtin-top.c:1120
> #13 0x00007ffff6e7dba8 in start_thread (arg=<optimized out>) at pthread_create.c:448
> #14 0x00007ffff6f01b8c in __GI___clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:78
>
> The cause is that perf_env__find_br_cntr_info tries to access a
> null pointer pmu_caps in the perf_env struct. A similar issue exists
> for homogeneous core systems which use the cpu_pmu_caps structure.
>
> Fix this by populating cpu_pmu_caps and pmu_caps structures with
> values from sysfs when calling perf top with branch stack sampling
> enabled.
>
> [1], LBR event logging introduced here:
> https://lore.kernel.org/all/20231025201626.3000228-5-kan.liang@linux.intel.com/
>
> Signed-off-by: Thomas Falcon <thomas.falcon@...el.com>
Reviewed-by: Ian Rogers <irogers@...gle.com>
Thanks!
Ian
> ---
> v3: constify struct perf_pmu *pmu in __perf_env__read_core_pmu_caps()
> use perf_pmus__find_core_pmu() instead of perf_pmus__scan_core(NULL)
>
> v2: update commit message with more meaningful stack trace from
> gdb and indicate that affected systems are limited to CPU's
> with LBR event logging support and that both hybrid and
> non-hybrid core systems are affected.
> ---
> tools/perf/builtin-top.c | 8 +++
> tools/perf/util/env.c | 114 +++++++++++++++++++++++++++++++++++++++
> tools/perf/util/env.h | 1 +
> 3 files changed, 123 insertions(+)
>
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index f9f31391bddb..c9d679410591 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -1729,6 +1729,14 @@ int cmd_top(int argc, const char **argv)
> if (opts->branch_stack && callchain_param.enabled)
> symbol_conf.show_branchflag_count = true;
>
> + if (opts->branch_stack) {
> + status = perf_env__read_core_pmu_caps(&perf_env);
> + if (status) {
> + pr_err("PMU capability data is not available\n");
> + goto out_delete_evlist;
> + }
> + }
> +
> sort__mode = SORT_MODE__TOP;
> /* display thread wants entries to be collapsed in a different tree */
> perf_hpp_list.need_collapse = 1;
> diff --git a/tools/perf/util/env.c b/tools/perf/util/env.c
> index 36411749e007..6735786a1d22 100644
> --- a/tools/perf/util/env.c
> +++ b/tools/perf/util/env.c
> @@ -416,6 +416,120 @@ static int perf_env__read_nr_cpus_avail(struct perf_env *env)
> return env->nr_cpus_avail ? 0 : -ENOENT;
> }
>
> +static int __perf_env__read_core_pmu_caps(const struct perf_pmu *pmu,
> + int *nr_caps, char ***caps,
> + unsigned int *max_branches,
> + unsigned int *br_cntr_nr,
> + unsigned int *br_cntr_width)
> +{
> + struct perf_pmu_caps *pcaps = NULL;
> + char *ptr, **tmp;
> + int ret = 0;
> +
> + *nr_caps = 0;
> + *caps = NULL;
> +
> + if (!pmu->nr_caps)
> + return 0;
> +
> + *caps = zalloc(sizeof(char *) * pmu->nr_caps);
> + if (!*caps)
> + return -ENOMEM;
> +
> + tmp = *caps;
> + list_for_each_entry(pcaps, &pmu->caps, list) {
> +
> + if (asprintf(&ptr, "%s=%s", pcaps->name, pcaps->value) < 0) {
> + ret = -ENOMEM;
> + goto error;
> + }
> +
> + *tmp++ = ptr;
> +
> + if (!strcmp(pcaps->name, "branches"))
> + *max_branches = atoi(pcaps->value);
> +
> + if (!strcmp(pcaps->name, "branch_counter_nr"))
> + *br_cntr_nr = atoi(pcaps->value);
> +
> + if (!strcmp(pcaps->name, "branch_counter_width"))
> + *br_cntr_width = atoi(pcaps->value);
> + }
> + *nr_caps = pmu->nr_caps;
> + return 0;
> +error:
> + while (tmp-- != *caps)
> + free(*tmp);
> + free(*caps);
> + *caps = NULL;
> + *nr_caps = 0;
> + return ret;
> +}
> +
> +int perf_env__read_core_pmu_caps(struct perf_env *env)
> +{
> + struct perf_pmu *pmu = NULL;
> + struct pmu_caps *pmu_caps;
> + int nr_pmu = 0, i = 0, j;
> + int ret;
> +
> + nr_pmu = perf_pmus__num_core_pmus();
> +
> + if (!nr_pmu)
> + return -ENODEV;
> +
> + if (nr_pmu == 1) {
> + pmu = perf_pmus__find_core_pmu();
> + if (!pmu)
> + return -ENODEV;
> + ret = perf_pmu__caps_parse(pmu);
> + if (ret < 0)
> + return ret;
> + return __perf_env__read_core_pmu_caps(pmu, &env->nr_cpu_pmu_caps,
> + &env->cpu_pmu_caps,
> + &env->max_branches,
> + &env->br_cntr_nr,
> + &env->br_cntr_width);
> + }
> +
> + pmu_caps = zalloc(sizeof(*pmu_caps) * nr_pmu);
> + if (!pmu_caps)
> + return -ENOMEM;
> +
> + while ((pmu = perf_pmus__scan_core(pmu)) != NULL) {
> + if (perf_pmu__caps_parse(pmu) <= 0)
> + continue;
> + ret = __perf_env__read_core_pmu_caps(pmu, &pmu_caps[i].nr_caps,
> + &pmu_caps[i].caps,
> + &pmu_caps[i].max_branches,
> + &pmu_caps[i].br_cntr_nr,
> + &pmu_caps[i].br_cntr_width);
> + if (ret)
> + goto error;
> +
> + pmu_caps[i].pmu_name = strdup(pmu->name);
> + if (!pmu_caps[i].pmu_name) {
> + ret = -ENOMEM;
> + goto error;
> + }
> + i++;
> + }
> +
> + env->nr_pmus_with_caps = nr_pmu;
> + env->pmu_caps = pmu_caps;
> +
> + return 0;
> +error:
> + for (i = 0; i < nr_pmu; i++) {
> + for (j = 0; j < pmu_caps[i].nr_caps; j++)
> + free(pmu_caps[i].caps[j]);
> + free(pmu_caps[i].caps);
> + free(pmu_caps[i].pmu_name);
> + }
> + free(pmu_caps);
> + return ret;
> +}
> +
> const char *perf_env__raw_arch(struct perf_env *env)
> {
> return env && !perf_env__read_arch(env) ? env->arch : "unknown";
> diff --git a/tools/perf/util/env.h b/tools/perf/util/env.h
> index d90e343cf1fa..135a1f714905 100644
> --- a/tools/perf/util/env.h
> +++ b/tools/perf/util/env.h
> @@ -152,6 +152,7 @@ struct btf_node;
>
> extern struct perf_env perf_env;
>
> +int perf_env__read_core_pmu_caps(struct perf_env *env);
> void perf_env__exit(struct perf_env *env);
>
> int perf_env__kernel_is_64_bit(struct perf_env *env);
> --
> 2.49.0
>
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