cgroup: avoid accessing modular cgroup subsys structure without locking
subsys[i] is set to NULL in cgroup_unload_subsys() at modular unload,
and that's protected by cgroup_mutex, and then the memory *subsys[i]
resides will be freed.
So this is unsafe without any locking:
if (!ss || ss->module)
...
v2:
- add a comment for enum cgroup_subsys_id
- simplify the comment in cgroup_exit()
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 75c6ec1..5f76829 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -44,14 +44,25 @@
extern const struct file_operations proc_cgroup_operations;
-/* Define the enumeration of all builtin cgroup subsystems */
+/*
+ * Define the enumeration of all cgroup subsystems.
+ *
+ * We define ids for builtin subsystems and then modular ones.
+ */
#define SUBSYS(_x) _x ## _subsys_id,
-#define IS_SUBSYS_ENABLED(option) IS_ENABLED(option)
enum cgroup_subsys_id {
+#define IS_SUBSYS_ENABLED(option) IS_BUILTIN(option)
#include <linux/cgroup_subsys.h>
+#undef IS_SUBSYS_ENABLED
+ CGROUP_BUILTIN_SUBSYS_COUNT,
+
+ __CGROUP_SUBSYS_TEMP_PLACEHOLDER = CGROUP_BUILTIN_SUBSYS_COUNT - 1,
+
+#define IS_SUBSYS_ENABLED(option) IS_MODULE(option)
+#include <linux/cgroup_subsys.h>
+#undef IS_SUBSYS_ENABLED
CGROUP_SUBSYS_COUNT,
};
-#undef IS_SUBSYS_ENABLED
#undef SUBSYS
/* Per-subsystem/per-cgroup state maintained by the system. */