[PATCH v5 0/8] Add generic support for relaxed atomics

From: Will Deacon
Date: Thu Aug 06 2015 - 12:56:15 EST


Hi all,

Here is version five of the patches previously posted here:

v1: https://lwn.net/Articles/650862/
v2: https://lwn.net/Articles/651293/
v3: https://lwn.net/Articles/652369/
v4: https://lwn.net/Articles/653388/

The 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.

Changes since v4 are:

* Drop the ret_t macro parameter in favour of typeof tricks (Peter Z)

* Add a missing acquire to the qrwlock code, as it was based on a
previous patch that I posted (Waiman Long)

Build tested on ARM, arm64, PowerPC and x86.

All feedback welcome,

Will

--->8

Will Deacon (8):
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: implement queue_write_unlock using smp_store_release
locking/qrwlock: make use of acquire/release/relaxed atomics
include/llist: use linux/atomic.h instead of asm/cmpxchg.h
ARM: atomics: define our SMP atomics in terms of _relaxed operations

arch/arm/include/asm/atomic.h | 37 ++---
arch/arm/include/asm/cmpxchg.h | 47 +-----
arch/x86/include/asm/qrwlock.h | 10 --
include/asm-generic/atomic-long.h | 263 +++++++++++--------------------
include/asm-generic/qrwlock.h | 22 +--
include/linux/atomic.h | 323 ++++++++++++++++++++++++++++++++++++++
include/linux/llist.h | 2 +-
kernel/locking/qrwlock.c | 22 ++-
lib/lockref.c | 8 -
9 files changed, 462 insertions(+), 272 deletions(-)

--
2.1.4

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