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Message-ID: <1528721717.2289.114.camel@codethink.co.uk>
Date: Mon, 11 Jun 2018 13:55:17 +0100
From: Ben Hutchings <ben.hutchings@...ethink.co.uk>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Vlastimil Babka <vbabka@...e.cz>,
Andrea Arcangeli <aarcange@...hat.com>,
Michal Hocko <mhocko@...nel.org>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
Catalin Marinas <catalin.marinas@....com>,
David Daney <david.daney@...ium.com>,
David Miller <davem@...emloft.net>,
"H. Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
Ingo Molnar <mingo@...nel.org>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Nitin Gupta <nitin.m.gupta@...cle.com>,
Ralf Baechle <ralf@...ux-mips.org>,
Thomas Gleixner <tglx@...utronix.de>,
Vineet Gupta <vgupta@...opsys.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Sasha Levin <alexander.levin@...rosoft.com>
Subject: Re: [PATCH 4.4 051/268] asm-generic: provide
generic_pmdp_establish()
On Mon, 2018-05-28 at 12:00 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>
> [ Upstream commit c58f0bb77ed8bf93dfdde762b01cb67eebbdfc29 ]
>
> Patch series "Do not lose dirty bit on THP pages", v4.
>
> Vlastimil noted that pmdp_invalidate() is not atomic and we can lose
> dirty and access bits if CPU sets them after pmdp dereference, but
> before set_pmd_at().
>
> The bug can lead to data loss, but the race window is tiny and I haven't
> seen any reports that suggested that it happens in reality. So I don't
> think it worth sending it to stable.
[...]
> This patch (of 12):
>
> This is an implementation of pmdp_establish() that is only suitable for
> an architecture that doesn't have hardware dirty/accessed bits. In this
> case we can't race with CPU which sets these bits and non-atomic
> approach is fine.
[...]
There's no point in applying just this patch, since it adds a new
function that nothing will call.
I tend to think that since this is fixing a potential data loss, the
whole series should be backported. But the commit message here says it
shouldn't.
Ben.
--
Ben Hutchings, Software Developer Codethink Ltd
https://www.codethink.co.uk/ Dale House, 35 Dale Street
Manchester, M1 2HF, United Kingdom
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