perf pmus: Add placeholder core PMU

If loading a core PMU fails, legacy hardware/cache events may segv due
to there being no PMU. Create a placeholder empty PMU for this
case. This was discussed in:
https://lore.kernel.org/lkml/20230614151625.2077-1-yangjihong1@huawei.com/

Reported-by: Yang Jihong <yangjihong1@huawei.com>
Tested-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: James Clark <james.clark@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/r/20230627182834.117565-1-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index 8d5ecd4ff1a91788f66da1893cda40482e0546ed..7f984a7f16ca2636120dd547720113f8774a66ee 100644 (file)
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -928,6 +928,31 @@ err:
        return NULL;
 }
 
+/* Creates the PMU when sysfs scanning fails. */
+struct perf_pmu *perf_pmu__create_placeholder_core_pmu(struct list_head *core_pmus)
+{
+       struct perf_pmu *pmu = zalloc(sizeof(*pmu));
+
+       if (!pmu)
+               return NULL;
+
+       pmu->name = strdup("cpu");
+       if (!pmu->name) {
+               free(pmu);
+               return NULL;
+       }
+
+       pmu->is_core = true;
+       pmu->type = PERF_TYPE_RAW;
+       pmu->cpus = cpu_map__online();
+
+       INIT_LIST_HEAD(&pmu->format);
+       INIT_LIST_HEAD(&pmu->aliases);
+       INIT_LIST_HEAD(&pmu->caps);
+       list_add_tail(&pmu->list, core_pmus);
+       return pmu;
+}
+
 void perf_pmu__warn_invalid_formats(struct perf_pmu *pmu)
 {
        struct perf_pmu_format *format;

diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
index 8807a624e918109cdb6b2fa291ca81e22c7dd1d1..203b92860e3cec8cdc940e477b6a606d509c9f42 100644 (file)
--- a/tools/perf/util/pmu.h
+++ b/tools/perf/util/pmu.h
@@ -286,6 +286,7 @@ int perf_pmu__event_source_devices_fd(void);
 int perf_pmu__pathname_fd(int dirfd, const char *pmu_name, const char *filename, int flags);
 
 struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char *lookup_name);
+struct perf_pmu *perf_pmu__create_placeholder_core_pmu(struct list_head *core_pmus);
 void perf_pmu__delete(struct perf_pmu *pmu);
 
 #endif /* __PMU_H */

diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
index 0866dee3fc62e8d8ce937cc63a0af331b67e4fba..3cd9de42139ea77f0733b8c9c0728ffcf69277f1 100644 (file)
--- a/tools/perf/util/pmus.c
+++ b/tools/perf/util/pmus.c
@@ -153,7 +153,12 @@ static void pmu_read_sysfs(bool core_only)
 
        closedir(dir);
        if (core_only) {
-               read_sysfs_core_pmus = true;
+               if (!list_empty(&core_pmus))
+                       read_sysfs_core_pmus = true;
+               else {
+                       if (perf_pmu__create_placeholder_core_pmu(&core_pmus))
+                               read_sysfs_core_pmus = true;
+               }
        } else {
                read_sysfs_core_pmus = true;
                read_sysfs_all_pmus = true;