[PATCHv4 0/9] ACCESS_ONCE and non-scalar accesses

From: Christian Borntraeger
Date: Wed Dec 03 2014 - 17:33:14 EST

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
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(-)


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