linux-kernel - Re: [PATCH] mm/hugetlb: use pmd_page() in follow_huge

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Message-ID: <alpine.DEB.2.10.1504091235500.11370@chino.kir.corp.google.com>
Date:	Thu, 9 Apr 2015 12:41:47 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Gerald Schaefer <gerald.schaefer@...ibm.com>
cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Michal Hocko <mhocko@...e.cz>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH] mm/hugetlb: use pmd_page() in follow_huge_pmd()

On Thu, 9 Apr 2015, Gerald Schaefer wrote:

> commit 61f77eda "mm/hugetlb: reduce arch dependent code around follow_huge_*"
> broke follow_huge_pmd() on s390, where pmd and pte layout differ and using
> pte_page() on a huge pmd will return wrong results. Using pmd_page() instead
> fixes this.
> 
> All architectures that were touched by commit 61f77eda have pmd_page()
> defined, so this should not break anything on other architectures.
> 
> Signed-off-by: Gerald Schaefer <gerald.schaefer@...ibm.com>
> Cc: stable@...r.kernel.org # v3.12

Acked-by: David Rientjes <rientjes@...gle.com>

I'm not sure where the stable cc came from, though: commit 61f77eda makes 
s390 use a generic version of follow_huge_pmd() and that generic version 
is buggy for s930 because of commit e66f17ff7177 ("mm/hugetlb: take page 
table lock in follow_huge_pmd()").  Both of those are 4.0 material, 
though, so why is this needed for stable 3.12?
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