cgroup: drop task_lock() protection around task->cgroups

For optimization, task_lock() is additionally used to protect
task->cgroups.  The optimization is pretty dubious as either
css_set_rwsem is grabbed anyway or PF_EXITING already protects
task->cgroups.  It adds only overhead and confusion at this point.
Let's drop task_[un]lock() and update comments accordingly.

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

1 files changed, 4 insertions, 2 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 4829a577c1b9..acbb9a4cb6e9 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -658,10 +658,12 @@ struct cgroup_subsys_state *css_parent(struct cgroup_subsys_state *css)
  */
 #ifdef CONFIG_PROVE_RCU
 extern struct mutex cgroup_mutex;
+extern struct rw_semaphore css_set_rwsem;
 #define task_css_set_check(task, __c)                                   \
         rcu_dereference_check((task)->cgroups,                          \
-                lockdep_is_held(&(task)->alloc_lock) ||                 \
-                lockdep_is_held(&cgroup_mutex) || (__c))
+                lockdep_is_held(&cgroup_mutex) ||                       \
+                lockdep_is_held(&css_set_rwsem) ||                      \
+                ((task)->flags & PF_EXITING) || (__c))
 #else
 #define task_css_set_check(task, __c)                                   \
         rcu_dereference((task)->cgroups)