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Subject: Re: [PATCH] mm/gup: check page posion status for coredump.
To:     Aili Yao <yaoaili@kingsoft.com>, akpm@linux-foundation.org,
        naoya.horiguchi@nec.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        yangfeng1@kingsoft.com, sunhao2@kingsoft.com,
        Oscar Salvador <osalvador@suse.de>,
        Mike Kravetz <mike.kravetz@oracle.com>
References: <20210317163714.328a038d@alex-virtual-machine>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <20a0d078-f49d-54d6-9f04-f6b41dd51e5f@redhat.com>
Date:   Wed, 17 Mar 2021 10:12:02 +0100
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On 17.03.21 09:37, Aili Yao wrote:
> When we do coredump for user process signal, this may be an SIGBUS signal
> with BUS_MCEERR_AR or BUS_MCEERR_AO code, which means this signal is
> resulted from ECC memory fail like SRAR or SRAO, we expect the memory
> recovery work is finished correctly, then the get_dump_page() will not
> return the error page as its process pte is set invalid by
> memory_failure().
> 
> But memory_failure() may fail, and the process's related pte may not be
> correctly set invalid, for current code, we will return the poison page
> and get it dumped and lead to system panic as its in kernel code.
> 
> So check the poison status in get_dump_page(), and if TRUE, return NULL.
> 
> Signed-off-by: Aili Yao <yaoaili@kingsoft.com>
> ---
>   mm/gup.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index e4c224c..499a496 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1536,6 +1536,14 @@ struct page *get_dump_page(unsigned long addr)
>   				      FOLL_FORCE | FOLL_DUMP | FOLL_GET);
>   	if (locked)
>   		mmap_read_unlock(mm);
> +
> +	if (IS_ENABLED(CONFIG_MEMORY_FAILURE) && ret == 1) {
> +		if (unlikely(PageHuge(page) && PageHWPoison(compound_head(page))))
> +			ret = 0;
> +		else if (unlikely(PageHWPoison(page)))
> +			ret = 0;
> +	}

I wonder if a simple

if (PageHWPoison(compound_head(page)))
	ret = 0;

won't suffice. But I guess the "issue" is compound pages that are not 
huge pages or transparent huge pages.

If not, we certainly want a wrapper for that magic, otherwise we have to 
replicate the same logic all over the place.

> +
>   	return (ret == 1) ? page : NULL;
>   }
>   #endif /* CONFIG_ELF_CORE */
> 


-- 
Thanks,

David / dhildenb