linux-kernel - Re: [PATCH 2/4] mm/hwpoison: fix potential pte_unmap

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Message-ID: <20210817233701.GA485476@hori.linux.bs1.fc.nec.co.jp>
Date:   Tue, 17 Aug 2021 23:37:01 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Miaohe Lin <linmiaohe@...wei.com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] mm/hwpoison: fix potential pte_unmap_unlock pte error

On Tue, Aug 17, 2021 at 04:24:43PM +0800, Miaohe Lin wrote:
> On 2021/8/17 15:29, HORIGUCHI NAOYA(堀口 直也) wrote:
...
> > One question is that according to "grep -r pte_unmap_unlock ." command over
> > whole kernel source code, pte_unmap_unlock() is called with "ptep - 1" in some places.
> > I think that none of them seems to have "break in for loop" in locked period,
> > so the same problem does not occur there.  But I'm still not sure why some place
> > call with "ptep - 1" and the others call with pte returned by pte_offset_map_lock().
> 
> IMO pte_unmap_unlock() works as long as the passed in pte belongs to the same page returned
> from pte_offset_map_lock(). I have fixed some similar place where pte_unmap_unlock() is called
> with wrong "ptep - 1" when I was learning the related mm code.

Great, thanks for clarification.

- Naoya