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Message-ID: <6ffd38b54e57709ca980087abe2582f1ae89250c.camel@intel.com>
Date: Tue, 13 May 2025 17:17:07 +0000
From: "Falcon, Thomas" <thomas.falcon@...el.com>
To: "irogers@...gle.com" <irogers@...gle.com>
CC: "alexander.shishkin@...ux.intel.com" <alexander.shishkin@...ux.intel.com>,
"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
"peterz@...radead.org" <peterz@...radead.org>, "acme@...nel.org"
<acme@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>, "Hunter, Adrian"
<adrian.hunter@...el.com>, "namhyung@...nel.org" <namhyung@...nel.org>,
"jolsa@...nel.org" <jolsa@...nel.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "kan.liang@...ux.intel.com"
<kan.liang@...ux.intel.com>, "mark.rutland@....com" <mark.rutland@....com>
Subject: Re: [PATCH v2] perf top: populate PMU capabilities data in perf_env
On Tue, 2025-05-13 at 08:40 -0700, Ian Rogers wrote:
> On Thu, May 8, 2025 at 9:31 AM 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.
>
Hi Ian, thanks for reviewing!
> At some point we should add a `perf top` shell test and include
> regression tests for cases like this.
Good point, I will look into creating a test for this.
>
> > 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>
> > ---
> > 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 1061f4eebc3f..c2688e4ef3c4 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..37ed6dc52cf3 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(struct perf_pmu *pmu,
>
> Prefer "const struct perf_pmu *pmu" to show that it doesn't change within.
Ok, I will change that in a new version.
>
> > + 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__scan_core(NULL);
>
> There is perf_pmus__find_core_pmu for this, not sure why this is in
> pmu.h rather than pmus.h though.
Thanks, I will use perf_pmus__find_core_pmu() for this then. Should I include another patch moving
the prototype to pmus.h?
Tom
>
> Thanks,
> Ian
>
> > + 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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