linux-kernel - Re: Arm64 crash while online/offline memory sections

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Message-ID: <20210526071948.GA30891@linux>
Date:   Wed, 26 May 2021 09:20:19 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     David Hildenbrand <david@...hat.com>
Cc:     "Qian Cai (QUIC)" <quic_qiancai@...cinc.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Arm64 crash while online/offline memory sections

On Tue, May 25, 2021 at 08:12:22PM +0200, David Hildenbrand wrote:
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index b31b3af5c490..6e661d106e96 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -218,14 +218,15 @@ static int memory_block_offline(struct memory_block *mem)
>         struct zone *zone;
>         int ret;
> -       zone = page_zone(pfn_to_page(start_pfn));
> -
>         /*
>          * Unaccount before offlining, such that unpopulated zone and kthreads
>          * can properly be torn down in offline_pages().
>          */
> -       if (nr_vmemmap_pages)
> +       if (nr_vmemmap_pages) {
> +               /* Hotplugged memory has no holes. */
> +               zone = page_zone(pfn_to_page(start_pfn));
>                 adjust_present_page_count(zone, -nr_vmemmap_pages);
> +       }
>         ret = offline_pages(start_pfn + nr_vmemmap_pages,
>                             nr_pages - nr_vmemmap_pages);
> 
> 
> We must not touch pfn_to_page(start_pfn) if it might be a memory hole.
> offline_pages() will make sure there are no holes, but that's too late.

Yeah, definitely. I somehow didn't think about holes when writing that.
Thanks for catching it David. Would you be so kind to send a patch?

Thanks!


-- 
Oscar Salvador
SUSE L3