Re: [PATCH v1 2/6] mm/hwpoison: remove race consideration

From: Ding Hui <dinghui@sangfor.com.cn>
To: Naoya Horiguchi <nao.horiguchi@gmail.com>, linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
	David Hildenbrand <david@redhat.com>,
	Oscar Salvador <osalvador@suse.de>,
	Michal Hocko <mhocko@suse.com>, Tony Luck <tony.luck@intel.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 2/6] mm/hwpoison: remove race consideration
Date: Tue, 15 Jun 2021 20:57:06 +0800	[thread overview]
Message-ID: <25c69dc8-0ce2-8330-dfb0-506481dc9a53@sangfor.com.cn> (raw)
In-Reply-To: <20210614021212.223326-3-nao.horiguchi@gmail.com>

On 2021/6/14 10:12, Naoya Horiguchi wrote:
> @@ -1956,17 +1938,6 @@ int unpoison_memory(unsigned long pfn)
>   		goto unlock_mutex;
>   	}
>   
> -	/*
> -	 * unpoison_memory() can encounter thp only when the thp is being
> -	 * worked by memory_failure() and the page lock is not held yet.
> -	 * In such case, we yield to memory_failure() and make unpoison fail.
> -	 */
> -	if (!PageHuge(page) && PageTransHuge(page)) {
> -		unpoison_pr_info("Unpoison: Memory failure is now running on %#lx\n",
> -				 pfn, &unpoison_rs);
> -		goto unlock_mutex;
> -	}
> -

if a huge page is in process of alloc or free, HUGETLB_PAGE_DTOR can be 
set after __SetPageHead() or be cleared before __ClearPageHead(), so 
this condition may be true in racy.

Do we need the racy test for this situation?

>   	if (!get_hwpoison_page(p, flags)) {
>   		if (TestClearPageHWPoison(p))
>   			num_poisoned_pages_dec();
-- 
Thanks,
- Ding Hui