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:
> +	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);