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

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Message-ID: <DM5PR0201MB35570CBA70B13484205FF9C28E259@DM5PR0201MB3557.namprd02.prod.outlook.com>
Date:   Tue, 25 May 2021 19:56:35 +0000
From:   "Qian Cai (QUIC)" <quic_qiancai@...cinc.com>
To:     David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>
CC:     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



> -----Original Message-----
> From: David Hildenbrand <david@...hat.com>
> Sent: Tuesday, May 25, 2021 2:12 PM
> I assume the following will work:
> 
> 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.

Good catch, David. This patch works well.