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Date:   Sun, 3 Jul 2022 18:42:59 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc:     linux-mm@kvack.org, David Hildenbrand <david@redhat.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Liu Shixin <liushixin2@huawei.com>,
        Yang Shi <shy828301@gmail.com>,
        Oscar Salvador <osalvador@suse.de>,
        Muchun Song <songmuchun@bytedance.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [mm-unstable PATCH v4 2/9] mm/hugetlb: separate path for
 hwpoison entry in copy_hugetlb_page_range()
Message-Id: <20220703184259.99a37313037000bd2e9ace9a@linux-foundation.org>
In-Reply-To: <20220704013312.2415700-3-naoya.horiguchi@linux.dev>
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        <20220704013312.2415700-3-naoya.horiguchi@linux.dev>
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On Mon,  4 Jul 2022 10:33:05 +0900 Naoya Horiguchi <naoya.horiguchi@linux.dev> wrote:

> Originally copy_hugetlb_page_range() handles migration entries and hwpoisoned
> entries in similar manner.  But recently the related code path has more code
> for migration entries, and when is_writable_migration_entry() was converted
> to !is_readable_migration_entry(), hwpoison entries on source processes got
> to be unexpectedly updated (which is legitimate for migration entries, but
> not for hwpoison entries).  This results in unexpected serious issues like
> kernel panic when forking processes with hwpoison entries in pmd.
> 
> Separate the if branch into one for hwpoison entries and one for migration
> entries.
> 
> ...
>
> Cc: <stable@vger.kernel.org> # 5.18

It's unusual to have a cc:stable patch in the middle of a series like
this.  One would expect the fix to be a standalone thing against
current -linus.

As presented, this patch won't get into mainline until after 5.20-rc1. 
If that's OK then OK.  Otherwise I can shuffle things around and stage
this patch in mm-hotfixes?