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Date:   Sun, 20 Feb 2022 23:43:18 +0000
From:   HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>
To:     Miaohe Lin <linmiaohe@...wei.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 v3 4/8] mm/memory-failure.c: fix race with changing page
 more robustly

On Fri, Feb 18, 2022 at 05:01:14PM +0800, Miaohe Lin wrote:
> We're only intended to deal with the non-Compound page after we split thp
> in memory_failure. However, the page could have changed compound pages due
> to race window. If this happens, we could retry once to hopefully handle
> the page next round. Also remove unneeded orig_head. It's always equal to
> the hpage. So we can use hpage directly and remove this redundant one.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

Acked-by: Naoya Horiguchi <naoya.horiguchi@....com>

> ---
>  mm/memory-failure.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 7e205d91b2d7..2ca50cfa601f 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1690,7 +1690,6 @@ int memory_failure(unsigned long pfn, int flags)
>  {
>  	struct page *p;
>  	struct page *hpage;
> -	struct page *orig_head;
>  	struct dev_pagemap *pgmap;
>  	int res = 0;
>  	unsigned long page_flags;
> @@ -1736,7 +1735,7 @@ int memory_failure(unsigned long pfn, int flags)
>  		goto unlock_mutex;
>  	}
>  
> -	orig_head = hpage = compound_head(p);
> +	hpage = compound_head(p);
>  	num_poisoned_pages_inc();
>  
>  	/*
> @@ -1817,10 +1816,21 @@ int memory_failure(unsigned long pfn, int flags)
>  	lock_page(p);
>  
>  	/*
> -	 * The page could have changed compound pages during the locking.
> -	 * If this happens just bail out.
> +	 * We're only intended to deal with the non-Compound page here.
> +	 * However, the page could have changed compound pages due to
> +	 * race window. If this happens, we could try again to hopefully
> +	 * handle the page next round.
>  	 */
> -	if (PageCompound(p) && compound_head(p) != orig_head) {
> +	if (PageCompound(p)) {
> +		if (retry) {
> +			if (TestClearPageHWPoison(p))
> +				num_poisoned_pages_dec();
> +			unlock_page(p);
> +			put_page(p);
> +			flags &= ~MF_COUNT_INCREASED;
> +			retry = false;
> +			goto try_again;
> +		}
>  		action_result(pfn, MF_MSG_DIFFERENT_COMPOUND, MF_IGNORED);
>  		res = -EBUSY;
>  		goto unlock_page;
> -- 
> 2.23.0

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