Merge branch 'for-5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup updates from Tejun Heo:
 "Two minor changes.

  One makes cgroup interface files ignore zero-sized writes rather than
  triggering -EINVAL on them. The other change is a cleanup which
  doesn't cause any behavior changes"

* 'for-5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: Zero sized write should be no-op
  cgroup: remove redundant kernfs_activate in cgroup_setup_root()

Author: torvalds

kernel/cgroup/cgroup.c

@@ -2006,7 +2006,6 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
 	BUG_ON(!list_empty(&root_cgrp->self.children));
 	BUG_ON(atomic_read(&root->nr_cgrps) != 1);
 
-	kernfs_activate(root_cgrp->kn);
 	ret = 0;
 	goto out;
 
@@ -3682,6 +3681,9 @@ static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
 	struct cgroup_subsys_state *css;
 	int ret;
 
+	if (!nbytes)
+		return 0;
+
 	/*
 	 * If namespaces are delegation boundaries, disallow writes to
 	 * files in an non-init namespace root from inside the namespace