linux-kernel - [PATCH v2 0/8] cleanup: Introduce ACQUIRE(), a guard() for conditional locks

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Message-ID: <20250619050416.782871-1-dan.j.williams@intel.com>
Date: Wed, 18 Jun 2025 22:04:08 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: <linux-cxl@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, Alison Schofield
	<alison.schofield@...el.com>, Dave Jiang <dave.jiang@...el.com>, "David
 Lechner" <dlechner@...libre.com>, Davidlohr Bueso <dave@...olabs.net>, "Fabio
 M. De Francesco" <fabio.maria.de.francesco@...ux.intel.com>, "Fabio M . De
 Francesco" <fabio.m.de.francesco@...ux.intel.com>, Ingo Molnar
	<mingo@...nel.org>, Ira Weiny <ira.weiny@...el.com>, Jonathan Cameron
	<jonathan.cameron@...wei.com>, Linus Torvalds
	<torvalds@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>,
	"Shiju Jose" <shiju.jose@...wei.com>, Vishal Verma <vishal.l.verma@...el.com>
Subject: [PATCH v2 0/8] cleanup: Introduce ACQUIRE(), a guard() for conditional locks

Changes since v1: [1]
* Peter took one look at v1 and rewrote it into something significantly
  better. Unlike my attempt that required suffering a new parallel
  universe of lock guards, the rewrite reuses existing lock guards.
  ACQUIRE() can be used any place guard() can be used, and adds
  ACQUIRE_ERR() to pass the result of conditional locks.

[1]: http://lore.kernel.org/20250507072145.3614298-1-dan.j.williams@intel.com

Note, all the code in patch1 is Peter's I just wrapped it in a changelog
and added some commentary. Peter, forgive me if you were still in the
process of circling back to this topic. I marked the patch attributed to
you as: "Not-yet-signed-off-by". Otherwise, my motivation for going
ahead with a formal submission are the multiple patchsets in my review /
development queue where I would like to use ACQUIRE().

The orginal motivation of v1 for this work is that the CXL subsystem
adopted scope-based helpers and achieved some decent cleanups. However,
that work stalled with conditional locks. It stalled due to the pain
points of scoped_cond_guard() detailed in patch1.

This work also allows for replacing open-coded equivalents like
rwsem_read_intr_acquire() that went upstream in v6.16:

    0c6e6f1357cb cxl/edac: Add CXL memory device patrol scrub control feature

The open question from the discussion [2] was whether it was worth
defining a __GUARD_IS_ERR() asm helper. I left that alone.

Lastly, this version of ACQUIRE_ERR() matches Peter's original proposal
to have the caller pass the lock scope variable by reference [3]. My
change of heart came from looking at the conversion and wanting
ACQUIRE_ERR() to be more visually distinct from ACQUIRE() especially
because it is accessing lock condition metadata, not the lock itself.

E.g.

       ACQUIRE(rwsem_read_intr, rwsem)(&cxl_rwsem.region);
       if ((ret = ACQUIRE_ERR(rwsem_read_intr, &rwsem)))
               return ret;

Yes, checkpatch disagrees with assignment in if(), but cleanup.h already
demands other expections for historical style, and a compact / limited
idiom for ACQUIRE_ERR() feels reasonable.

[2]: http://lore.kernel.org/20250514064624.GA24938@noisy.programming.kicks-ass.net
[3]: http://lore.kernel.org/20250512105026.GP4439@noisy.programming.kicks-ass.net

Dan Williams (7):
  cxl/mbox: Convert poison list mutex to ACQUIRE()
  cxl/decoder: Move decoder register programming to a helper
  cxl/decoder: Drop pointless locking
  cxl/region: Split commit_store() into __commit() and queue_reset()
    helpers
  cxl/region: Move ready-to-probe state check to a helper
  cxl/region: Introduce CLASS(cxl_decoder_detach...) consolidate
    multiple paths
  cxl: Convert to ACQUIRE() for conditional rwsem locking

Peter Zijlstra (1):
  cleanup: Introduce ACQUIRE() and ACQUIRE_ERR() for conditional locks

 drivers/cxl/core/cdat.c   |   6 +-
 drivers/cxl/core/core.h   |  60 +++++-
 drivers/cxl/core/edac.c   |  44 ++--
 drivers/cxl/core/hdm.c    | 118 +++++-----
 drivers/cxl/core/mbox.c   |  13 +-
 drivers/cxl/core/memdev.c |  50 ++---
 drivers/cxl/core/port.c   |  24 +--
 drivers/cxl/core/region.c | 443 +++++++++++++++++++-------------------
 drivers/cxl/cxl.h         |  13 +-
 drivers/cxl/cxlmem.h      |   4 +-
 include/linux/cleanup.h   |  77 +++++--
 include/linux/mutex.h     |   2 +-
 include/linux/rwsem.h     |   3 +-
 13 files changed, 460 insertions(+), 397 deletions(-)

base-commit: e04c78d86a9699d136910cfc0bdcf01087e3267e
-- 
2.49.0