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

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Date:   Wed, 22 Aug 2018 13:19:59 +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:
> +	downgrade_write(&mm->mmap_sem);
> +
> +	/* Zap mappings with read mmap_sem */
> +	unmap_region(mm, start_vma, prev, start, end);
> +
> +	arch_unmap(mm, start_vma, start, end);

Hmm, did you check that all architectures' arch_unmap() is safe with
read mmap_sem instead of write mmap_sem? E.g. x86 does
mpx_notify_unmap() there where I would be far from sure at first glance...

> +	remove_vma_list(mm, start_vma);
> +	up_read(&mm->mmap_sem);