perf symbols: Set freed members to NULL in dso destructor

To help in debugging use after free bugs.

Reported-by: Ingo Molnar <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/dso.c

···
 	int i;
 	for (i = 0; i < MAP__NR_TYPES; ++i)
 		symbols__delete(&dso->symbols[i]);
-	if (dso->short_name_allocated)
+
+	if (dso->short_name_allocated) {
 		free((char *)dso->short_name);
-	if (dso->long_name_allocated)
+		dso->short_name		  = NULL;
+		dso->short_name_allocated = false;
+	}
+
+	if (dso->long_name_allocated) {
 		free((char *)dso->long_name);
+		dso->long_name		 = NULL;
+		dso->long_name_allocated = false;
+	}
+
 	dso_cache__free(&dso->cache);
 	dso__free_a2l(dso);
 	free(dso->symsrc_filename);
+	dso->symsrc_filename = NULL;
 	free(dso);
 }