linux-kernel - Re: [PATCH] mm: memory-failure: fix unexpected return value in soft_offline

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Date:   Wed, 28 Jun 2023 09:56:38 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <naoya.horiguchi@....com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: memory-failure: fix unexpected return value in
 soft_offline_page()

On 2023/6/28 3:30, Andrew Morton wrote:
> On Tue, 27 Jun 2023 19:28:08 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:
> 
>> When page_handle_poison() fails to handle the hugepage or free page in
>> retry path, soft_offline_page() will return 0 while -EBUSY is expected
>> in this case.
> 
> What are the user visible effects of the bug?

The user will think soft_offline_page succeeds while it failed in fact. So user
will not try again later in this case.

> 
>> Fixes: b94e02822deb ("mm,hwpoison: try to narrow window race for free pages")
>>
>> ...
>>
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -2737,10 +2737,13 @@ int soft_offline_page(unsigned long pfn, int flags)
>>  	if (ret > 0) {
>>  		ret = soft_offline_in_use_page(page);
>>  	} else if (ret == 0) {
>> -		if (!page_handle_poison(page, true, false) && try_again) {
>> -			try_again = false;
>> -			flags &= ~MF_COUNT_INCREASED;
>> -			goto retry;
>> +		if (!page_handle_poison(page, true, false)) {
>> +			if (try_again) {
>> +				try_again = false;
>> +				flags &= ~MF_COUNT_INCREASED;
>> +				goto retry;
>> +			}
>> +			ret = -EBUSY;
>>  		}
>>  	}
> .
>