RE: Arm64 crash while online/offline memory sections

["Qian Cai (QUIC)" <quic_qiancai@quicinc.com>]

> -----Original Message-----
> From: David Hildenbrand <david@redhat.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.