[PATCHv5 0/8] ACCESS_ONCE and non-scalar accesses

From: Christian Borntraeger
Date: Thu Dec 11 2014 - 09:05:40 EST

As discussed on LKML http://marc.info/?i=54611D86.4040306%40de.ibm.com
ACCESS_ONCE might fail with specific compilers 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.

Due to all the trouble when dealing with linux-next, I will defer the patch
that forces ACCESS_ONCE to work only on scalar types after rc1 to give it
a full spin in linux-next.

If nobody complains I will ask Linus to pull this for 3.19 next week.
The tree can be found at

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

1. READ_ONCE/ASSIGN_ONCE use x instead of p
2. linux/types.h --> uapi/linux/types.h u??-->__u?? to avoid header
inclusion fun and compile errors
3. Actually provide data_access_exceeds_word_size.
4. also move handle_pte_fault to a barrier as there is ppc44x which has
64bit ptes and 32bit word size. Some sanity check from a VM person
would be good.

Cc: linux-mm@xxxxxxxxx

Christian Borntraeger (8):
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 barrier fixup with READ_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 | 18 ++++------
arch/x86/include/asm/spinlock.h | 8 ++---
arch/x86/mm/gup.c | 2 +-
include/linux/compiler.h | 70 +++++++++++++++++++++++++++++++++++++++
lib/Makefile | 2 +-
lib/access.c | 8 +++++
mm/gup.c | 2 +-
mm/memory.c | 11 +++++-
mm/rmap.c | 3 +-
12 files changed, 108 insertions(+), 26 deletions(-)
create mode 100644 lib/access.c


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/