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Subject: Re: [PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to
 the order when onlining
To:     linux-kernel@vger.kernel.org
Cc:     linux-mm@kvack.org, Arun KS <arunks@codeaurora.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        Pavel Tatashin <pasha.tatashin@soleen.com>,
        Dan Williams <dan.j.williams@intel.com>
References: <20190814154109.3448-1-david@redhat.com>
 <20190814154109.3448-5-david@redhat.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <b47ebf69-77eb-4a77-0fbc-631175aca979@redhat.com>
Date:   Wed, 14 Aug 2019 18:09:16 +0200
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On 14.08.19 17:41, David Hildenbrand wrote:
> Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher
> order") assumed that any PFN we get via memory resources is aligned to
> to MAX_ORDER - 1, I am not convinced that is always true. Let's play safe,
> check the alignment and fallback to single pages.
> 
> Cc: Arun KS <arunks@codeaurora.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  mm/memory_hotplug.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 63b1775f7cf8..f245fb50ba7f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>  	 */
>  	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
>  		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
> +		/* __free_pages_core() wants pfns to be aligned to the order */
> +		if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
> +			order = 0;
>  		(*online_page_callback)(pfn_to_page(pfn), order);
>  	}
>  
> 

@Michal, if you insist, we can drop this patch. "break first and fix
later" is not part of my DNA :)

-- 

Thanks,

David / dhildenb