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)
...
Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
---
include/linux/cgroup.h | 11 +++++++++--
kernel/cgroup.c | 32 ++++++++++++++++++--------------
2 files changed, 27 insertions(+), 16 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 75c6ec1..3ac6bb0 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -46,12 +46,19 @@ extern const struct file_operations proc_cgroup_operations;
/* Define the enumeration of all builtin cgroup subsystems */
#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. */
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f4554cc..29273db 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4944,17 +4944,17 @@ void cgroup_post_fork(struct task_struct *child)
* and addition to css_set.
*/
if (need_forkexit_callback) {
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ /*
+ * fork/exit callbacks are supported only for builtin
+ * subsystems, and the builtin section of the subsys
+ * array is immutable, so we don't need to lock the
+ * subsys array here. On the other hand, modular section
+ * of the array can be freed at module unload, so we
+ * can't touch that.
+ */
+ for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
- /*
- * fork/exit callbacks are supported only for
- * builtin subsystems and we don't need further
- * synchronization as they never go away.
- */
- if (!ss || ss->module)
- continue;
-
if (ss->fork)
ss->fork(child);
}
@@ -5019,13 +5019,17 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
tsk->cgroups = &init_css_set;
if (run_callbacks && need_forkexit_callback) {
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ /*
+ * fork/exit callbacks are supported only for builtin
+ * subsystems, and the builtin section of the subsys
+ * array is immutable, so we don't need to lock the
+ * subsys array here. On the other hand, modular section
+ * of the array can be freed at module unload, so we
+ * can't touch that.
+ */
+ for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
- /* modular subsystems can't use callbacks */
- if (!ss || ss->module)
- continue;
-
if (ss->exit) {
struct cgroup *old_cgrp =
rcu_dereference_raw(cg->subsys[i])->cgroup;
--
1.8.0.2
--
To unsubscribe from this list: send the line "unsubscribe cgroups" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
