linux-kernel - Re: [PATCH] mm/sparsemem: pfn_to_page is not valid yet on SPARSEMEM

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Date:   Sun, 9 Feb 2020 18:36:49 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     akpm@...ux-foundation.org, osalvador@...e.de,
        dan.j.williams@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, david@...hat.com
Subject: Re: [PATCH] mm/sparsemem: pfn_to_page is not valid yet on SPARSEMEM

On 02/06/20 at 08:53pm, Wei Yang wrote:
> When we use SPARSEMEM instead of SPARSEMEM_VMEMMAP, pfn_to_page()
> doesn't work before sparse_init_one_section() is called. This leads to a
> crash when hotplug memory.
> 
> We should use memmap as it did.

A good fix, thanks.

Reviewed-by: Baoquan He <bhe@...hat.com>

By the way, the failure trace should be added to log so that people can
know better what happened. And this happened in hot adding side in
SPARSEMEM|!VMEMMAP case, the hot removing failed too in this case, I
will psot patch to fix it right away.

> 
> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
> CC: Dan Williams <dan.j.williams@...el.com>
> ---
>  mm/sparse.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 5a8599041a2a..2efb24ff8f96 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -882,7 +882,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>  	 * Poison uninitialized struct pages in order to catch invalid flags
>  	 * combinations.
>  	 */
> -	page_init_poison(pfn_to_page(start_pfn), sizeof(struct page) * nr_pages);
> +	page_init_poison(memmap, sizeof(struct page) * nr_pages);
>  
>  	ms = __nr_to_section(section_nr);
>  	set_section_nid(section_nr, nid);
> -- 
> 2.17.1
>