linux-kernel - Re: [PATCHv4 0/9] ACCESS_ONCE and non-scalar accesses

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Date:	Thu, 04 Dec 2014 16:24:02 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	linux-kernel@...r.kernel.org
CC:	linux-arch@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	torvalds@...ux-foundation.org
Subject: Re: [PATCHv4 0/9] ACCESS_ONCE and non-scalar accesses

Am 03.12.2014 um 23:30 schrieb Christian Borntraeger:
> As discussed on LKML http://marc.info/?i=54611D86.4040306%40de.ibm.com
> ACCESS_ONCE might fail with specific compiler for non-scalar accesses.
> 
> Here is a set of patches to tackle that problem.
> 
> The first patch introduce READ_ONCE and ASSIGN_ONCE. If the data structure
> is larger than the machine word size memcpy is used and a warning is emitted.
> The next patches fix up all in-tree users of ACCESS_ONCE on non-scalar types.
> The last patch forces ACCESS_ONCE to work only on scalar types. 
> 
> I have cross-compiled the resulting kernel with defconfig and gcc 4.9 for
> microblaze, m68k, alpha, s390,x86_64, i686, sparc, sparc64, mips,
> ia64, arm and arm64.
> 
> Runtime tested on s390x and x86_64. I have also verified that ASSIGN_ONCE works
> as expected with some test changes as there are no user in this patch series.
> 
> Linus, ok for the next merge window?
> 
> Christian Borntraeger (9):
>   kernel: Provide READ_ONCE and ASSIGN_ONCE
>   mm: replace ACCESS_ONCE with READ_ONCE or barriers
>   x86/spinlock: Replace ACCESS_ONCE with READ_ONCE
>   x86/gup: Replace ACCESS_ONCE with READ_ONCE
>   mips/gup: Replace ACCESS_ONCE with READ_ONCE
>   arm64/spinlock: Replace ACCESS_ONCE READ_ONCE
>   arm/spinlock: Replace ACCESS_ONCE with READ_ONCE
>   s390/kvm: REPLACE ACCESS_ONCE with READ_ONCE
>   kernel: tighten rules for ACCESS ONCE
> 
>  arch/arm/include/asm/spinlock.h   |  4 +--
>  arch/arm64/include/asm/spinlock.h |  4 +--
>  arch/mips/mm/gup.c                |  2 +-
>  arch/s390/kvm/gaccess.c           | 14 ++++----
>  arch/x86/include/asm/spinlock.h   |  8 ++---
>  arch/x86/mm/gup.c                 |  2 +-
>  include/linux/compiler.h          | 74 ++++++++++++++++++++++++++++++++++++++-
>  mm/gup.c                          |  2 +-
>  mm/memory.c                       |  2 +-
>  mm/rmap.c                         |  3 +-
>  10 files changed, 95 insertions(+), 20 deletions(-)
> 

FWIW, the code is on

git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux.git linux-next
and
git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux.git ACCESS_ONCE

I rebased the queue against rc3 + the initial patch that triggered the  whole discussion.

Christian

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