linux-kernel - [PATCH v1 1/2] perf evsel: Ensure the fallback message is always written to

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Message-ID: <20250918172416.1247940-1-irogers@google.com>
Date: Thu, 18 Sep 2025 10:24:15 -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>, 
	Howard Chu <howardchu95@...il.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v1 1/2] perf evsel: Ensure the fallback message is always
 written to

The fallback message is unconditionally printed in places like
record__open. If no fallback is attempted this can lead to printing
uninitialized data, crashes, etc.

Fixes: c0a54341c0e8 ("perf evsel: Introduce event fallback method")
Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/evsel.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 477cddf08c5c..814ef6f6b32a 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -3565,7 +3565,7 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
 
 		/* If event has exclude user then don't exclude kernel. */
 		if (evsel->core.attr.exclude_user)
-			return false;
+			goto no_fallback;
 
 		/* Is there already the separator in the name. */
 		if (strchr(name, '/') ||
@@ -3573,7 +3573,7 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
 			sep = "";
 
 		if (asprintf(&new_name, "%s%su", name, sep) < 0)
-			return false;
+			goto no_fallback;
 
 		free(evsel->name);
 		evsel->name = new_name;
@@ -3596,17 +3596,19 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
 			sep = "";
 
 		if (asprintf(&new_name, "%s%sH", name, sep) < 0)
-			return false;
+			goto no_fallback;
 
 		free(evsel->name);
 		evsel->name = new_name;
 		/* Apple M1 requires exclude_guest */
-		scnprintf(msg, msgsize, "trying to fall back to excluding guest samples");
+		scnprintf(msg, msgsize, "Trying to fall back to excluding guest samples");
 		evsel->core.attr.exclude_guest = 1;
 
 		return true;
 	}
-
+no_fallback:
+	scnprintf(msg, msgsize, "No fallback found for '%s' for error %d",
+		  evsel__name(evsel), err);
 	return false;
 }
 
-- 
2.51.0.470.ga7dc726c21-goog