perf symbols: only set vmlinux longname & mark loaded if really loaded

dso__load_vmlinux() uses the filename passed to it to directly set the
dso long_name, which resulted in a use after free due to
dso__load_vmlinux_path() treating 0 symbols as a load failure and
subsequently freeing the contents of dso->long_name.

Change dso__load_vmlinux() so that finding 0 symbols does not cause it
to consider itself loaded, and do not set long_name in such a case.

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Cc: David Hansen <dave@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Matt Hellsley <matthltc@us.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1344637382-22789-9-git-send-email-cody@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol.c

@@ -1364,13 +1364,14 @@ int dso__load_vmlinux(struct dso *dso, struct map *map,
 	if (fd < 0)
 		return -1;
 
-	dso__set_long_name(dso, (char *)vmlinux);
-	dso__set_loaded(dso, map->type);
 	err = dso__load_sym(dso, map, symfs_vmlinux, fd, filter, 0, 0);
 	close(fd);
 
-	if (err > 0)
+	if (err > 0) {
+		dso__set_long_name(dso, (char *)vmlinux);
+		dso__set_loaded(dso, map->type);
 		pr_debug("Using %s for symbols\n", symfs_vmlinux);
+	}
 
 	return err;
 }