linux-kernel - Re: [RFC v8 PATCH 3/5] mm: mmap: zap pages with read mmap

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Date:   Wed, 22 Aug 2018 13:11:03 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Yang Shi <yang.shi@...ux.alibaba.com>, mhocko@...nel.org,
        willy@...radead.org, ldufour@...ux.vnet.ibm.com,
        kirill@...temov.name, akpm@...ux-foundation.org,
        peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC v8 PATCH 3/5] mm: mmap: zap pages with read mmap_sem in
 munmap

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?