linux-kernel - Re: [PATCH 2/4] mm: memory-failure: fix potential unexpected return value from unpoison

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Message-ID: <20230719234851.GA1583723@ik1-406-35019.vs.sakura.ne.jp>
Date:   Thu, 20 Jul 2023 08:48:51 +0900
From:   Naoya Horiguchi <naoya.horiguchi@...ux.dev>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, naoya.horiguchi@....com,
        shy828301@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mm: memory-failure: fix potential unexpected return
 value from unpoison_memory()

On Sat, Jul 15, 2023 at 11:17:27AM +0800, Miaohe Lin wrote:
> If unpoison_memory() fails to clear page hwpoisoned flag, return value
> ret is expected to be -EBUSY. But when get_hwpoison_page() returns 1
> and fails to clear page hwpoisoned flag due to races, return value will
> be unexpected 1 leading to users being confused.

Thank you for fixing this.

> 
> Fixes: bf181c582588 ("mm/hwpoison: fix unpoison_memory()")
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/memory-failure.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 9ab97016877e..ac074f82f5b3 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2546,11 +2546,11 @@ int unpoison_memory(unsigned long pfn)
>  			unpoison_pr_info("Unpoison: failed to grab page %#lx\n",
>  					 pfn, &unpoison_rs);
>  	} else {
> +		ret = -EBUSY;

It seems be a code smell to me that the variable "ret" is used not only to
save the return value of unpoison_memory(), but also to save the return
value from get_hwpoison_page(). So I think that it might be better to use
another auto-variable solely to save the return value of get_hwpoison_page.
Then ret has the initial value -EBUSY at this point and no need to
reinitialize it.

Thanks,
Naoya Horiguchi

>  		if (PageHuge(p)) {
>  			huge = true;
>  			count = folio_free_raw_hwp(folio, false);
>  			if (count == 0) {
> -				ret = -EBUSY;
>  				folio_put(folio);
>  				goto unlock_mutex;
>  			}
> -- 
> 2.33.0
> 
> 
>