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**Apache Airflow version**: 2.0.2 and 2.1.1

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**OS**: Debian

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**Apache Airflow Provider versions**: 
apache-airflow-providers-ftp==2.0.0
apache-airflow-providers-imap==2.0.0
apache-airflow-providers-sqlite==2.0.0

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**Deployment**: docker-compose

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**What happened**:

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**What you expected to happen**:

Permissions for subdags should get listed on list roles on Airflow UI but only the parent dag get listed but not the children dags.

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**How to reproduce it**:

Run airflow 2.0.2 or 2.1.1 with a subdag in the dags directory. And then try to find subdag listing on list roles on Airflow UI.

![subdag_not_listed](https://user-images.githubusercontent.com/9834450/129717365-9620895e-9876-4ac2-8adb-fc448183a78b.png)


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**Anything else we need to know**:
It appears this problem is there most of the time.
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airflow/www/security.py
"""Sync the provided roles and permissions."""
        existing_roles = self._get_all_roles_with_permissions()
        non_dag_perms = self._get_all_non_dag_permissions()
        for config in roles:
            role_name = config['role']
            perms = config['perms']
            role = existing_roles.get(role_name) or self.add_role(role_name)
            for action_name, resource_name in perms:
                perm = non_dag_perms.get((action_name, resource_name)) or self.create_permission(
                    action_name, resource_name
                )
                if perm not in role.permissions:
                    self.add_permission_to_role(role, perm)
    def add_permissions(self, role, perms):
        """Adds permissions to a given role."""
        for action_name, resource_name in perms:
            permission = self.create_permission(action_name, resource_name)
            self.add_permission_to_role(role, permission)
    def get_resource(self, name: str) -> ViewMenu:
        """
        Returns a resource record by name, if it exists.
        :param name: Name of resource
        :type name: str
        :return: Resource record
        :rtype: ViewMenu
        """
        return self.find_view_menu(name)
    def get_all_resources(self) -> List[ViewMenu]: