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Date:   Tue, 26 Feb 2019 16:51:56 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     zhong jiang <zhongjiang@huawei.com>
Cc:     n-horiguchi@ah.jp.nec.com, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org, mhocko@suse.com,
        hughd@google.com, mhocko@kernel.org
Subject: Re: [PATCH] mm: hwpoison: fix thp split handing in
 soft_offline_in_use_page()
Message-ID: <20190226135156.mifspmbdyr6m3hff@kshutemo-mobl1>
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On Tue, Feb 26, 2019 at 07:18:00PM +0800, zhong jiang wrote:
> From: zhongjiang <zhongjiang@huawei.com>
> 
> When soft_offline_in_use_page() runs on a thp tail page after pmd is plit,

s/plit/split/

> we trigger the following VM_BUG_ON_PAGE():
> 
> Memory failure: 0x3755ff: non anonymous thp
> __get_any_page: 0x3755ff: unknown zero refcount page type 2fffff80000000
> Soft offlining pfn 0x34d805 at process virtual address 0x20fff000
> page:ffffea000d360140 count:0 mapcount:0 mapping:0000000000000000 index:0x1
> flags: 0x2fffff80000000()
> raw: 002fffff80000000 ffffea000d360108 ffffea000d360188 0000000000000000
> raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
> page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0)
> ------------[ cut here ]------------
> kernel BUG at ./include/linux/mm.h:519!
> 
> soft_offline_in_use_page() passed refcount and page lock from tail page to
> head page, which is not needed because we can pass any subpage to
> split_huge_page().

I don't see a description of what is going wrong and why change will fixed
it. From the description, it appears as it's cosmetic-only change.

Please elaborate.

-- 
 Kirill A. Shutemov