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Subject: Re: [PATCH v2 2/2] mm/memory-failure.c: Don't access uninitialized
 memmaps in memory_failure()
To:     linux-kernel@vger.kernel.org
Cc:     linux-mm@kvack.org, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>
References: <20191009142435.3975-1-david@redhat.com>
 <20191009142435.3975-3-david@redhat.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <1c61f433-74a0-73ca-0a8b-9ac7252ec6f8@redhat.com>
Date:   Mon, 14 Oct 2019 10:41:30 +0200
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On 09.10.19 16:24, 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@ah.jp.nec.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Signed-off-by: David Hildenbrand <david@redhat.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);
>   	if (PageHuge(p))
>   		return memory_failure_hugetlb(pfn, flags);
>   	if (TestSetPageHWPoison(p)) {
> 

@Andrew, can you add

Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319

And

Cc: stable@vger.kernel.org # v4.13+

The stable backports won't be clean cherry-picks AFAIKS, but do-able.

-- 

Thanks,

David / dhildenb