linux-kernel - Re: [PATCH v2 2/2] mm/memory-failure.c: Don't access uninitialized memmaps in memory

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Date:   Thu, 10 Oct 2019 00:26:19 +0000
From:   Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:     David Hildenbrand <david@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH v2 2/2] mm/memory-failure.c: Don't access uninitialized
 memmaps in memory_failure()

On Wed, Oct 09, 2019 at 04:24:35PM +0200, David Hildenbrand wrote:
> We should check for pfn_to_online_page() to not access uninitialized
> memmaps. Reshuffle the code so we don't have to duplicate the error
> message.
> 
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  mm/memory-failure.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 7ef849da8278..e866e6e5660b 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1253,17 +1253,19 @@ int memory_failure(unsigned long pfn, int flags)
>  	if (!sysctl_memory_failure_recovery)
>  		panic("Memory failure on page %lx", pfn);
>  
> -	if (!pfn_valid(pfn)) {
> +	p = pfn_to_online_page(pfn);
> +	if (!p) {
> +		if (pfn_valid(pfn)) {
> +			pgmap = get_dev_pagemap(pfn, NULL);
> +			if (pgmap)
> +				return memory_failure_dev_pagemap(pfn, flags,
> +								  pgmap);
> +		}
>  		pr_err("Memory failure: %#lx: memory outside kernel control\n",
>  			pfn);
>  		return -ENXIO;
>  	}
>  
> -	pgmap = get_dev_pagemap(pfn, NULL);
> -	if (pgmap)
> -		return memory_failure_dev_pagemap(pfn, flags, pgmap);
> -
> -	p = pfn_to_page(pfn);

This change seems to assume that memory_failure_dev_pagemap() is never
called for online pages. Is it an intended behavior?
Or the concept "online pages" is not applicable to zone device pages?

Thanks,
Naoya Horiguchi