[PATCH 0/5] Add generic support for relaxed atomics

Will Deacon
2015-07-13T12:31:22Z

Hello,

This patch series adds support for a family of relaxed atomics to the
kernel. More specifically:

- acquire/release/relaxed flavours of xchg, cmpxchg and {add,sub}_return
- atomic_read_acquire
- atomic_set_release

This came out of a separate patch series porting the (barrier-heavy)
qrwlock code to arm64. Rather than have arch-specific hooks littered
around the place, it makes more sense to define a core set of relaxed
atomics that can be used regardless of architecture.

For now, the definitions simply take on the existing (i.e. full-barrier)
semantics, but there is a direct mapping onto arm64 and even architectures
with explicit memory barrier instructions (e.g. powerpc, arm) can benefit,
as they do from the existing smp_load_acquire/smp_store_release macros.

The final patch is a proof-of-concept port of the qrwlock over to the
new atomics. It's based on some of the pending patches from me and Waiman,
so it won't apply to mainline but I think it illustrates the usage well
enough.

All feedback welcome,

Will

--->8

Will Deacon (5):
atomics: add acquire/release/relaxed variants of some atomic
operations
asm-generic: rework atomic-long.h to avoid bulk code duplication
asm-generic: add relaxed/acquire/release variants for atomic_long_t
lockref: remove homebrew cmpxchg64_relaxed macro definition
locking/qrwlock: make use of acquire/release/relaxed atomics

Documentation/atomic_ops.txt | 4 +-
include/asm-generic/atomic-long.h | 263 ++++++++++++++------------------------
include/asm-generic/qrwlock.h | 13 +-
include/linux/atomic.h | 140 ++++++++++++++++++++
kernel/locking/qrwlock.c | 12 +-
lib/lockref.c | 8 --
6 files changed, 248 insertions(+), 192 deletions(-)

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2.1.4