static int cgroup_procs_write_permission(struct cgroup *src_cgrp,
					 struct cgroup *dst_cgrp,
					 struct super_block *sb,
					 struct cgroup_namespace *ns)
{
	struct cgroup *com_cgrp = src_cgrp;
	int ret;

	lockdep_assert_held(&cgroup_mutex);

	/* find the common ancestor */
	while (!cgroup_is_descendant(dst_cgrp, com_cgrp))
		com_cgrp = cgroup_parent(com_cgrp);

	/* %current should be authorized to migrate to the common ancestor */
	ret = cgroup_may_write(com_cgrp, sb);
	if (ret)
		return ret;

	/*
	 * If namespaces are delegation boundaries, %current must be able
	 * to see both source and destination cgroups from its namespace.
	 */
	if ((cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE) &&
	    (!cgroup_is_descendant(src_cgrp, ns->root_cset->dfl_cgrp) ||
	     !cgroup_is_descendant(dst_cgrp, ns->root_cset->dfl_cgrp)))
		return -ENOENT;

	return 0;
}
static int cgroup_procs_write_permission(struct cgroup *src_cgrp,
					 struct cgroup *dst_cgrp,
					 struct super_block *sb,
					 struct cgroup_namespace *ns)
{
	struct cgroup *com_cgrp = src_cgrp;
	int ret;

	lockdep_assert_held(&cgroup_mutex);

	 
	while (!cgroup_is_descendant(dst_cgrp, com_cgrp))
		com_cgrp = cgroup_parent(com_cgrp);

	 
	ret = cgroup_may_write(com_cgrp, sb);
	if (ret)
		return ret;

	 
	if ((cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE) &&
	    (!cgroup_is_descendant(src_cgrp, ns->root_cset->dfl_cgrp) ||
	     !cgroup_is_descendant(dst_cgrp, ns->root_cset->dfl_cgrp)))
		return -ENOENT;

	return 0;
}