perf probe: Fix dso->nsinfo refcounting

[ Upstream commit dedeb4b ]

ASan reports a memory leak of nsinfo during the execution of:

 # perf test "31: Lookup mmap thread".

The leak is caused by a refcounted variable being replaced without
dropping the refcount.

This patch makes sure that the refcnt of nsinfo is decreased whenever
a refcounted variable is replaced with a new value.

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
Fixes: 544abd4 ("perf probe: Allow placing uprobes in alternate namespaces.")
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Krister Johansen <kjlx@templeofstupid.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/55223bc8821b34ccb01f92ef1401c02b6a32e61f.1626343282.git.rickyman7@gmail.com
[ Split from a larger patch ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

tools/perf/util/probe-event.c

@@ -180,8 +180,10 @@ struct map *get_target_map(const char *target, struct nsinfo *nsi, bool user)
 		struct map *map;
 
 		map = dso__new_map(target);
-		if (map && map->dso)
+		if (map && map->dso) {
+			nsinfo__put(map->dso->nsinfo);
 			map->dso->nsinfo = nsinfo__get(nsi);
+		}
 		return map;
 	} else {
 		return kernel_get_module_map(target);