linux-kernel - [PATCH v1 10/15] perf pmu: Tolerate failure to read the type for wellknown PMUs

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Message-ID: <20250611034529.508842-11-irogers@google.com>
Date: Tue, 10 Jun 2025 20:45:24 -0700
From: Ian Rogers <irogers@...gle.com>
To: 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>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, James Clark <james.clark@...aro.org>, 
	Xu Yang <xu.yang_2@....com>, John Garry <john.g.garry@...cle.com>, 
	"Masami Hiramatsu (Google)" <mhiramat@...nel.org>, Howard Chu <howardchu95@...il.com>, 
	Weilin Wang <weilin.wang@...el.com>, Thomas Richter <tmricht@...ux.ibm.com>, 
	Andi Kleen <ak@...ux.intel.com>, Tiezhu Yang <yangtiezhu@...ngson.cn>, 
	Gautam Menghani <gautam@...ux.ibm.com>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org
Subject: [PATCH v1 10/15] perf pmu: Tolerate failure to read the type for
 wellknown PMUs

If sysfs isn't mounted then we may fail to read a PMU's type. In this
situation resort to lookup of wellknown types. Only applies to
software, tracepoint and breakpoint PMUs.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/pmu.c | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index 609828513f6c..4164c2278051 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -1181,6 +1181,32 @@ int perf_pmu__init(struct perf_pmu *pmu, __u32 type, const char *name)
 	return 0;
 }
 
+static __u32 wellknown_pmu_type(const char *pmu_name)
+{
+	struct {
+		const char *pmu_name;
+		__u32 type;
+	} wellknown_pmus[] = {
+		{
+			"software",
+			PERF_TYPE_SOFTWARE
+		},
+		{
+			"tracepoint",
+			PERF_TYPE_TRACEPOINT
+		},
+		{
+			"breakpoint",
+			PERF_TYPE_BREAKPOINT
+		},
+	};
+	for (size_t i = 0; i < ARRAY_SIZE(wellknown_pmus); i++) {
+		if (!strcmp(wellknown_pmus[i].pmu_name, pmu_name))
+			return wellknown_pmus[i].type;
+	}
+	return PERF_TYPE_MAX;
+}
+
 struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char *name,
 				  bool eager_load)
 {
@@ -1200,8 +1226,12 @@ struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char
 	 * that type value is successfully assigned (return 1).
 	 */
 	if (perf_pmu__scan_file_at(pmu, dirfd, "type", "%u", &pmu->type) != 1) {
-		perf_pmu__delete(pmu);
-		return NULL;
+		/* Double check the PMU's name isn't wellknown. */
+		pmu->type = wellknown_pmu_type(name);
+		if (pmu->type == PERF_TYPE_MAX) {
+			perf_pmu__delete(pmu);
+			return NULL;
+		}
 	}
 
 	/*
-- 
2.50.0.rc0.642.g800a2b2222-goog