linux-kernel - Re: [PATCH v3] mm/hotplug: invalid PFNs from pfn_to_online

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Message-ID: <20190122065818.GA4087@dhcp22.suse.cz>
Date:   Tue, 22 Jan 2019 07:58:18 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Qian Cai <cai@....pw>
Cc:     akpm@...ux-foundation.org, osalvador@...e.de,
        catalin.marinas@....com, vbabka@...e.cz, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm/hotplug: invalid PFNs from pfn_to_online_page()

On Mon 21-01-19 16:27:47, Qian Cai wrote:
[...]

Sorry to miss this before but you want to

> +#define pfn_to_online_page(pfn)					   \
> +({								   \
> +	struct page *___page = NULL;				   \
	unsigned long ___pfn = pfn;
> +	unsigned long ___nr = pfn_to_section_nr(pfn);		   \
			      pfn_to_section_nr(___pfn);
> +								   \
> +	if (___nr < NR_MEM_SECTIONS && online_section_nr(___nr) && \
> +	    pfn_valid_within(pfn))				   \
	    pfn_valid_within(___pfn))
	
> +		___page = pfn_to_page(pfn);			   \
> +	___page;						   \
>  })

to prevent from issues when pfn expression has side effects.
-- 
Michal Hocko
SUSE Labs