perf cpumap: Add checking for reference counter

For the CPU map merging test, add an extra check for the reference
counter before releasing the last CPU map.

Reviewed-by: Adrian Hunter <[e-mail]>
Signed-off-by: Leo Yan <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/tests/cpumap.c

···
 	cpu_map__snprint(a, buf, sizeof(buf));
 	TEST_ASSERT_VAL("failed to merge map: bad result", !strcmp(buf, expected));
 	perf_cpu_map__put(b);
+
+	/*
+	 * If 'b' is a superset of 'a', 'a' points to the same map with the
+	 * map 'b'. In this case, the owner 'b' has released the resource above
+	 * but 'a' still keeps the ownership, the reference counter should be 1.
+	 */
+	TEST_ASSERT_VAL("unexpected refcnt: bad result",
+			refcount_read(perf_cpu_map__refcnt(a)) == 1);
+
 	perf_cpu_map__put(a);
 	return 0;
 }