cgroup: Update out-of-date comment in cgroup_migrate()

Commit 674b745e22b3 ("cgroup: remove rcu_read_lock()/rcu_read_unlock()
in critical section of spin_lock_irq()") has removed the rcu_read_lock,
which makes the comment out-of-date, so update it.

tj: Updated the comment a bit.

Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 9d809191a54f1e9c86cd1fc05ba11a89372ac005..f329f49529a2c51afdc4ddee92a8a2743d782866 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2872,9 +2872,9 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup,
        struct task_struct *task;
 
        /*
-        * Prevent freeing of tasks while we take a snapshot. Tasks that are
-        * already PF_EXITING could be freed from underneath us unless we
-        * take an rcu_read_lock.
+        * The following thread iteration should be inside an RCU critical
+        * section to prevent tasks from being freed while taking the snapshot.
+        * spin_lock_irq() implies RCU critical section here.
         */
        spin_lock_irq(&css_set_lock);
        task = leader;