linux-kernel - Re: [PATCH] mm, hugetlb, soft_offline: save compound page order before page migration

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Message-Id: <20170912135448.341359676c6f8045f4a622f0@linux-foundation.org>
Date:   Tue, 12 Sep 2017 13:54:48 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexandru Moise <00moses.alexander00@...il.com>
Cc:     linux-kernel@...r.kernel.org, khandual@...ux.vnet.ibm.com,
        mhocko@...e.com, aarcange@...hat.com, minchan@...nel.org,
        hillf.zj@...baba-inc.com, shli@...com, rppt@...ux.vnet.ibm.com,
        kirill.shutemov@...ux.intel.com, mgorman@...hsingularity.net,
        rientjes@...gle.com, riel@...hat.com, linux-mm@...ck.org
Subject: Re: [PATCH] mm, hugetlb, soft_offline: save compound page order
 before page migration

On Tue, 12 Sep 2017 22:43:06 +0200 Alexandru Moise <00moses.alexander00@...il.com> wrote:

> This fixes a bug in madvise() where if you'd try to soft offline a
> hugepage via madvise(), while walking the address range you'd end up,
> using the wrong page offset due to attempting to get the compound
> order of a former but presently not compound page, due to dissolving
> the huge page (since c3114a8).

What are the user visible effects of the bug?  The wrong page is
offlined?  No offlining occurs?