cgroup: remove cgroup_lock_is_held()

We don't want controllers to assume that the information is officially
available and do funky things with it.

The only user is task_subsys_state_check() which uses it to verify RCU
access context.  We can move cgroup_lock_is_held() inside
CONFIG_PROVE_RCU but that doesn't add meaningful protection compared
to conditionally exposing cgroup_mutex.

Remove cgroup_lock_is_held(), export cgroup_mutex iff CONFIG_PROVE_RCU
and use lockdep_is_held() directly on the mutex in
task_subsys_state_check().

While at it, add parentheses around macro arguments in
task_subsys_state_check().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 63deb70f3149..515927eebb37 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -30,7 +30,6 @@ struct css_id;
 
 extern int cgroup_init_early(void);
 extern int cgroup_init(void);
-extern int cgroup_lock_is_held(void);
 extern void cgroup_fork(struct task_struct *p);
 extern void cgroup_post_fork(struct task_struct *p);
 extern void cgroup_exit(struct task_struct *p, int run_callbacks);
@@ -552,10 +551,16 @@ static inline struct cgroup_subsys_state *cgroup_subsys_state(
  * rcu_dereference_check() conditions, such as locks used during the
  * cgroup_subsys::attach() methods.
  */
+#ifdef CONFIG_PROVE_RCU
+extern struct mutex cgroup_mutex;
 #define task_subsys_state_check(task, subsys_id, __c)                   \
-        rcu_dereference_check(task->cgroups->subsys[subsys_id],         \
-                              lockdep_is_held(&task->alloc_lock) ||     \
-                              cgroup_lock_is_held() || (__c))
+        rcu_dereference_check((task)->cgroups->subsys[(subsys_id)],     \
+                              lockdep_is_held(&(task)->alloc_lock) ||   \
+                              lockdep_is_held(&cgroup_mutex) || (__c))
+#else
+#define task_subsys_state_check(task, subsys_id, __c)                   \
+        rcu_dereference((task)->cgroups->subsys[(subsys_id)])
+#endif
 
 static inline struct cgroup_subsys_state *
 task_subsys_state(struct task_struct *task, int subsys_id)