[PATCH v5 0/7] Introduce __xchg, non-atomic xchg

[Andrzej Hajda]

Hi all,

The helper is tiny and there are advices we can live without it, so
I want to present few arguments why it would be good to have it:

1. Code readability/simplification/number of lines:
  - decreases number of lines,
  - it often eliminates local variables,
  - for real examples see patches 3+.

2. Presence of similar helpers in other somehow related languages/libs:

a) Rust[1]: 'replace' from std::mem module, there is also 'take'
    helper (__xchg(&x, 0)), which is the same as private helper in
    i915 - fetch_and_zero, see latest patch.
b) C++ [2]: 'exchange' from utility header.

If the idea is OK there are still 2 questions to answer:

1. Name of the helper, __xchg follows kernel conventions,
    but for me Rust names are also OK.
2. Where to put the helper:
a) as in this patchset include/linux/non-atomic/xchg.h,
    proposed by Andy Shevchenko,
b) include/linux/utils.h ? any better name? Some kind
    of container for simple helpers.

All __xchg conversions were performed using cocci script,
then manually adjusted if necessary.

There is lot of places it can be used in, I have just chosen
some of them. I can provide cocci script to detect others (not all),
if necessary.

Changes:
v2: squashed all __xchg -> __arch_xchg t one patch (Arnd)
v3: fixed alpha/xchg_local (lkp at intel.com)
v4: adjusted indentation (Heiko)
v5: added more __xchg conversions - patches 3-6, added tags

[1]: https://doc.rust-lang.org/std/mem/index.html
[2]: https://en.cppreference.com/w/cpp/header/utility

Regards
Andrzej

Andrzej Hajda (7):
  arch: rename all internal names __xchg to __arch_xchg
  linux/include: add non-atomic version of xchg
  arch/*/uprobes: simplify arch_uretprobe_hijack_return_addr
  llist: simplify __llist_del_all
  io_uring: use __xchg if possible
  qed: use __xchg if possible
  drm/i915/gt: use __xchg instead of internal helper

 arch/alpha/include/asm/cmpxchg.h              | 10 +++++-----
 arch/arc/include/asm/cmpxchg.h                |  4 ++--
 arch/arm/include/asm/cmpxchg.h                |  7 ++++---
 arch/arm/probes/uprobes/core.c                |  8 ++------
 arch/arm64/include/asm/cmpxchg.h              |  7 +++----
 arch/arm64/kernel/probes/uprobes.c            |  9 ++-------
 arch/csky/kernel/probes/uprobes.c             |  9 ++-------
 arch/hexagon/include/asm/cmpxchg.h            | 10 +++++-----
 arch/ia64/include/asm/cmpxchg.h               |  2 +-
 arch/ia64/include/uapi/asm/cmpxchg.h          |  4 ++--
 arch/loongarch/include/asm/cmpxchg.h          |  4 ++--
 arch/m68k/include/asm/cmpxchg.h               |  6 +++---
 arch/mips/include/asm/cmpxchg.h               |  4 ++--
 arch/mips/kernel/uprobes.c                    | 10 ++--------
 arch/openrisc/include/asm/cmpxchg.h           | 10 +++++-----
 arch/parisc/include/asm/cmpxchg.h             |  4 ++--
 arch/powerpc/include/asm/cmpxchg.h            |  4 ++--
 arch/powerpc/kernel/uprobes.c                 | 10 ++--------
 arch/riscv/include/asm/atomic.h               |  2 +-
 arch/riscv/include/asm/cmpxchg.h              |  4 ++--
 arch/riscv/kernel/probes/uprobes.c            |  9 ++-------
 arch/s390/include/asm/cmpxchg.h               |  8 ++++----
 arch/s390/kernel/uprobes.c                    |  7 ++-----
 arch/sh/include/asm/cmpxchg.h                 |  4 ++--
 arch/sparc/include/asm/cmpxchg_32.h           |  4 ++--
 arch/sparc/include/asm/cmpxchg_64.h           |  6 +++---
 arch/sparc/kernel/uprobes.c                   |  7 ++-----
 arch/xtensa/include/asm/cmpxchg.h             |  4 ++--
 drivers/gpu/drm/i915/gt/intel_engine_cs.c     |  2 +-
 .../gpu/drm/i915/gt/intel_engine_heartbeat.c  |  4 ++--
 .../drm/i915/gt/intel_execlists_submission.c  |  4 ++--
 drivers/gpu/drm/i915/gt/intel_ggtt.c          |  4 ++--
 drivers/gpu/drm/i915/gt/intel_gsc.c           |  2 +-
 drivers/gpu/drm/i915/gt/intel_gt.c            |  4 ++--
 drivers/gpu/drm/i915/gt/intel_gt_pm.c         |  2 +-
 drivers/gpu/drm/i915/gt/intel_lrc.c           |  6 +++---
 drivers/gpu/drm/i915/gt/intel_migrate.c       |  2 +-
 drivers/gpu/drm/i915/gt/intel_rc6.c           |  2 +-
 drivers/gpu/drm/i915/gt/intel_rps.c           |  2 +-
 drivers/gpu/drm/i915/gt/selftest_context.c    |  2 +-
 .../drm/i915/gt/selftest_ring_submission.c    |  2 +-
 drivers/gpu/drm/i915/gt/selftest_timeline.c   |  2 +-
 drivers/gpu/drm/i915/gt/uc/intel_gsc_uc.c     |  2 +-
 drivers/gpu/drm/i915/gt/uc/intel_uc.c         |  2 +-
 drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c      |  2 +-
 drivers/gpu/drm/i915/i915_utils.h             |  1 +
 include/linux/llist.h                         |  6 ++----
 include/linux/non-atomic/xchg.h               | 19 +++++++++++++++++++
 include/linux/qed/qed_chain.h                 | 19 +++++++------------
 io_uring/io_uring.c                           |  7 ++-----
 io_uring/slist.h                              |  6 ++----
 51 files changed, 126 insertions(+), 155 deletions(-)
 create mode 100644 include/linux/non-atomic/xchg.h

-- 
2.34.1