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

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Message-Id: <20150410133859.fc79985a9514eb1e4d1dcde7@linux-foundation.org>
Date:	Fri, 10 Apr 2015 13:38:59 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Gerald Schaefer <gerald.schaefer@...ibm.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	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>,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH] mm/hugetlb: use pmd_page() in follow_huge_pmd()

On Fri, 10 Apr 2015 10:08:49 +0200 Gerald Schaefer <gerald.schaefer@...ibm.com> wrote:

> On Thu, 9 Apr 2015 12:41:47 -0700 (PDT)
> David Rientjes <rientjes@...gle.com> wrote:
> 
> > 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?
> 
> Both commits 61f77eda and e66f17ff already made it into the 3.12 stable
> tree, probably because of SLES 12 (actually that's how I noticed them).
> 
> But I guess I screwed up the stable CC, stable@...r.kernel.org.#.v3.12
> somehow doesn't look right, not sure if the CC in the patch header
> suffices. Looks like Jiri Slaby added the patches to 3.12, putting him
> on CC now.

hm.  I think I'll make it

Fixes: 61f77eda "mm/hugetlb: reduce arch dependent code around follow_huge_*"
...
Cc: <stable@...r.kernel.org>

There's enough info here for the various tree maintainers to work out
whether their kernel needs this fix.

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