linux-kernel - Re: [PATCH] mm/hwpoison: In-use hugepage need filter judgement and filter return value should be consistent

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Date:   Wed, 16 Feb 2022 01:44:13 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     luofei <luofei@...cloud.com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/hwpoison: In-use hugepage need filter judgement and
 filter return value should be consistent

On Thu, Feb 10, 2022 at 03:58:46AM -0500, luofei wrote:
> After successfully obtaining the reference count of the huge
> page, it is still necessary to call hwpoison_filter() to make a
> filter judgement, otherwise the filter page will be unmaped and
> the related process may be killed.
> 
> Also when the huge page meets the filter conditions, it should
> not be regarded as successful memory_failure() processing, but
> should return an error code to inform the caller, otherwise the
> caller regards the error page has been identified and isolated,
> which may lead to calling set_mce_nospec() to change page attribute.

Hi luofei,

I agree with inserting another hwpoison_filter() block which was
simply missed. Thanks for pointing it out.

> 
> Meanwhile, when calling hwpoison_filter() to determine that a page
> needs to be filtered, it is better to keep the same EBUSY return
> value, so that the caller can recognize that memory_failure() did
> not successfully process the error page.

IIRC, hwpoison_filter() is expected to ignore error events on
irrelevant target (page|device|cgroup) for testers to focus on
non-filtered events.  So filtered events should not be considered
as error-handling failures (otherwise testers can't easily
distinguish them from real error-handling failures).

But yes, the MCE handler depends on the return value of memory_failure(),
so filtered events shouldn't be considered as error-handling's successes.
So one possible approach is that we introduce a new mf_flags to show that
memory_failure() is called from MCE handler (not from hwpoison injector),
and we switch return code when hwpoison_filter failed by this flag.
Could you try it if this approach works for you?  Or if you have any better
idea, feel free to share it.

Thanks,
Naoya Horiguchi

> 
> Signed-off-by: luofei <luofei@...cloud.com>
> ---
>  mm/hwpoison-inject.c |  2 +-
>  mm/memory-failure.c  | 12 ++++++++++--
>  2 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
> index aff4d27ec235..4ecd77cd1ded 100644
> --- a/mm/hwpoison-inject.c
> +++ b/mm/hwpoison-inject.c
> @@ -44,7 +44,7 @@ static int hwpoison_inject(void *data, u64 val)
>  	 */
>  	err = hwpoison_filter(hpage);
>  	if (err)
> -		return 0;
> +		return -EBUSY;
>  
>  inject:
>  	pr_info("Injecting memory failure at pfn %#lx\n", pfn);
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 97a9ed8f87a9..acf97fb2659a 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1526,7 +1526,7 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>  				if (TestClearPageHWPoison(head))
>  					num_poisoned_pages_dec();
>  				unlock_page(head);
> -				return 0;
> +				return -EBUSY;
>  			}
>  			unlock_page(head);
>  			res = MF_FAILED;
> @@ -1545,6 +1545,13 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>  	lock_page(head);
>  	page_flags = head->flags;
>  
> +	if (hwpoison_filter(p)) {
> +		if (TestClearPageHWPoison(head))
> +			num_poisoned_pages_dec();
> +		unlock_page(head);
> +		res = -EBUSY
> +		goto out;
> +	}
>  	/*
>  	 * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
>  	 * simply disable it. In order to make it work properly, we need
> @@ -1613,7 +1620,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>  		goto out;
>  
>  	if (hwpoison_filter(page)) {
> -		rc = 0;
> +		rc = -EBUSY;
>  		goto unlock;
>  	}
>  
> @@ -1837,6 +1844,7 @@ int memory_failure(unsigned long pfn, int flags)
>  			num_poisoned_pages_dec();
>  		unlock_page(p);
>  		put_page(p);
> +		res = -EBUSY;
>  		goto unlock_mutex;
>  	}
>  
> -- 
> 2.27.0