linux-kernel - Re: [v11 PATCH 1/3] mm: mmap: zap pages with read mmap

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Date:   Wed, 26 Sep 2018 13:09:36 +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
Cc:     dave.hansen@...el.com, oleg@...hat.com, srikar@...ux.vnet.ibm.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v11 PATCH 1/3] mm: mmap: zap pages with read mmap_sem in munmap

On 9/19/18 7:03 PM, Yang Shi wrote:

...

> Suggested-by: Michal Hocko <mhocko@...nel.org>
> Suggested-by: Kirill A. Shutemov <kirill@...temov.name>
> Suggested-by: Matthew Wilcox <willy@...radead.org>
> Reviewed-by: Matthew Wilcox <willy@...radead.org>
> Cc: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>

This is indeed much better code structure. Thanks for persisting with
the series and following the suggestions.

Acked-by: Vlastimil Babka <vbabka@...e.cz>

Nit:

> @@ -2797,17 +2819,32 @@ int vm_munmap(unsigned long start, size_t len)
>  	if (down_write_killable(&mm->mmap_sem))
>  		return -EINTR;
>  
> -	ret = do_munmap(mm, start, len, &uf);
> -	up_write(&mm->mmap_sem);
> +	ret = __do_munmap(mm, start, len, &uf, downgrade);
> +	/*
> +	 * Returning 1 indicates mmap_sem is downgraded.
> +	 * But 1 is not legal return value of vm_munmap() and munmap(), reset
> +	 * it to 0 before return.
> +	 */
> +	if (ret == 1) {
> +		up_read(&mm->mmap_sem);
> +		ret = 0;
> +	} else
> +		up_write(&mm->mmap_sem);
> +

I think the else part should also have { } per the kernel style?