linux-kernel - [PATCH v1 2/4] libperf cpumap: Fix perf_cpu_map_

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Message-ID: <20251201230904.290733-2-irogers@google.com>
Date: Mon,  1 Dec 2025 15:09:02 -0800
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>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	James Clark <james.clark@...aro.org>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Cc: Ingo Molnar <mingo@...nel.org>
Subject: [PATCH v1 2/4] libperf cpumap: Fix perf_cpu_map__max for an
 empty/NULL map

Passing an empty map to perf_cpu_map__max triggered a SEGV. Explicitly
test for the empty map.

Reported-by: Ingo Molnar <mingo@...nel.org>
Closes: https://lore.kernel.org/linux-perf-users/aSwt7yzFjVJCEmVp@gmail.com/
Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/lib/perf/cpumap.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
index 7e88417ba84d..4160e7d2e120 100644
--- a/tools/lib/perf/cpumap.c
+++ b/tools/lib/perf/cpumap.c
@@ -368,10 +368,12 @@ struct perf_cpu perf_cpu_map__max(const struct perf_cpu_map *map)
 		.cpu = -1
 	};
 
-	// cpu_map__trim_new() qsort()s it, cpu_map__default_new() sorts it as well.
-	return __perf_cpu_map__nr(map) > 0
-		? __perf_cpu_map__cpu(map, __perf_cpu_map__nr(map) - 1)
-		: result;
+	if (!map)
+		return result;
+
+	// The CPUs are always sorted and nr is always > 0 as 0 length map is
+	// encoded as NULL.
+	return __perf_cpu_map__cpu(map, __perf_cpu_map__nr(map) - 1);
 }
 
 /** Is 'b' a subset of 'a'. */
-- 
2.52.0.158.g65b55ccf14-goog