struct mapped_device *dm_get_from_kobject(struct kobject *kobj)
{
	struct mapped_device *md;

	md = container_of(kobj, struct mapped_device, kobj_holder.kobj);

	spin_lock(&_minor_lock);
	if (test_bit(DMF_FREEING, &md->flags) || dm_deleting_md(md)) {
		md = NULL;
		goto out;
	}
	dm_get(md);
out:
	spin_unlock(&_minor_lock);

	return md;
}
The program contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.