cgroup: remove cgroup_mutex from cgroupstats_build

The function cgroupstats_build extracts cgroup from the kernfs_node's priv pointer which is a RCU pointer. So, there is no need to grab cgroup_mutex. Just get the reference on the cgroup before using and remove the cgroup_mutex altogether. Signed-off-by: Shakeel Butt <[email protected]> Signed-off-by: Tejun Heo <[email protected]>
niw · Oct 25, 2021 · bb75842 · bb75842
1 parent be28816
commit bb75842
Showing 1 changed file with 2 additions and 5 deletions.
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
@@ -698,18 +698,15 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 	    kernfs_type(kn) != KERNFS_DIR)
 		return -EINVAL;
 
-	mutex_lock(&cgroup_mutex);
-
 	/*
 	 * We aren't being called from kernfs and there's no guarantee on
 	 * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
 	 * @kn->priv is RCU safe.  Let's do the RCU dancing.
 	 */
 	rcu_read_lock();
 	cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
-	if (!cgrp || cgroup_is_dead(cgrp)) {
+	if (!cgrp || !cgroup_tryget(cgrp)) {
 		rcu_read_unlock();
-		mutex_unlock(&cgroup_mutex);
 		return -ENOENT;
 	}
 	rcu_read_unlock();
@@ -737,7 +734,7 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 	}
 	css_task_iter_end(&it);
 
-	mutex_unlock(&cgroup_mutex);
+	cgroup_put(cgrp);
 	return 0;
 }