Re: [RFC v8 PATCH 3/5] mm: mmap: zap pages with read mmap_sem in munmap

[Vlastimil Babka]

On 08/15/2018 08:49 PM, Yang Shi wrote:

> +	start_vma = munmap_lookup_vma(mm, start, end);
> +	if (!start_vma)
> +		goto out;
> +	if (IS_ERR(start_vma)) {
> +		ret = PTR_ERR(start_vma);
> +		goto out;
> +	}
> +
> +	prev = start_vma->vm_prev;
> +
> +	if (unlikely(uf)) {
> +		ret = userfaultfd_unmap_prep(start_vma, start, end, uf);
> +		if (ret)
> +			goto out;
> +	}
> +

You sure it's ok to redo this in case of goto regular path? The
preparations have some side-effects... I would rather move this after
the regular path check?