linux-kernel - Re: [PATCH 4/4] mm/hugeltb: handle the error case in hugetlb_fix_reserve

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Message-ID: <bc24856e-78ca-b44a-bf33-4b540720f72a@huawei.com>
Date:   Fri, 9 Apr 2021 15:07:00 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     Mike Kravetz <mike.kravetz@...cle.com>,
        <n-horiguchi@...jp.nec.com>, <hillf.zj@...baba-inc.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH 4/4] mm/hugeltb: handle the error case in
 hugetlb_fix_reserve_counts()

On 2021/4/9 13:04, Andrew Morton wrote:
> On Fri, 9 Apr 2021 11:17:49 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:
> 
>> On 2021/4/9 7:25, Mike Kravetz wrote:
>>> On 4/2/21 2:32 AM, Miaohe Lin wrote:
>>>> A rare out of memory error would prevent removal of the reserve map region
>>>> for a page. hugetlb_fix_reserve_counts() handles this rare case to avoid
>>>> dangling with incorrect counts. Unfortunately, hugepage_subpool_get_pages
>>>> and hugetlb_acct_memory could possibly fail too. We should correctly handle
>>>> these cases.
>>>
>>> Yes, this is a potential issue.
>>>
>>> The 'good news' is that hugetlb_fix_reserve_counts() is unlikely to ever
>>> be called.  To do so would imply we could not allocate a region entry
>>> which is only 6 words in size.  We also keep a 'cache' of entries so we
>>> may not even need to allocate.
>>>
>>> But, as mentioned it is a potential issue.
>>
>> Yes, a potential *theoretical* issue.
>>
>>>
>>>> Fixes: b5cec28d36f5 ("hugetlbfs: truncate_hugepages() takes a range of pages")
>>>
>>> This is likely going to make this get picked by by stable releases.
>>> That is unfortunate as mentioned above this is mostly theoretical.
>>>
>>
>> I will drop this. This does not worth backport.
>>
> 
> -stable have been asked not to backport MM patches unless MM patches
> include "cc:stable".  ie, no making our backporting decisions for us,
> please.
> 

Sorry about it! I would retain the Fixes tag.
Many thanks for pointing this out.

> .
>