[PATCH v3 hmm 06/12] mm/hmm: Hold on to the mmget for the lifetime of the range

[Christoph Hellwig]

>  	mutex_lock(&hmm->lock);
> -	list_del(&range->list);
> +	list_del_init(&range->list);
>  	mutex_unlock(&hmm->lock);

I don't see the point why this is a list_del_init - that just
reinitializeѕ range->list, but doesn't change anything for the list
head it was removed from.  (and if the list_del_init was intended
a later patch in your branch reverts it to plain list_del..)