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

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Message-Id: <20210408220453.f95942bf20baadd8dbbc1488@linux-foundation.org>
Date:   Thu, 8 Apr 2021 22:04:53 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
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 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.