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

On Wed, Jun 18, 2025 at 10:04:08PM -0700, Dan Williams wrote:

> 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().

Definitely a case of too many balls in the air. Feel free to make that
Signed-off-by, and also:

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

for the patches that were sent my way. Thanks for the changelogs and
pushing this ahead.

On Wed, Jun 18, 2025 at 10:04:08PM -0700, Dan Williams wrote:
> 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.

Hi Dan,

I've been building upon this set and applying this diff to squelch
those checkpatch ERRORs. Please take a look and consider adding for
review in next version.

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 664f7b7a622c..193a03fa7114 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -5682,7 +5682,14 @@ sub process {
 			my ($s, $c) = ($stat, $cond);
 			my $fixed_assign_in_if = 0;
 
-			if ($c =~ /\bif\s*\(.*[^<>!=]=[^=].*/s) {
+			if ($c =~ /\bif\s*\((.*[^<>!=]=[^=].*)\)/s) {
+				my $expr = $1;
+
+				# Allow ACQUIRE_ERR() special case
+				if ($expr =~ /\w+\s*=\s*ACQUIRE_ERR\s*\(/) {
+					next;
+				}
+
 				if (ERROR("ASSIGN_IN_IF",
 					  "do not use assignment in if condition\n" . $herecurr) &&
 				    $fix && $perl_version_ok) {



snip

Alison Schofield wrote:
> On Wed, Jun 18, 2025 at 10:04:08PM -0700, Dan Williams wrote:
> > 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.
> 
> Hi Dan,
> 
> I've been building upon this set and applying this diff to squelch
> those checkpatch ERRORs. Please take a look and consider adding for
> review in next version.
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 664f7b7a622c..193a03fa7114 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -5682,7 +5682,14 @@ sub process {
>  			my ($s, $c) = ($stat, $cond);
>  			my $fixed_assign_in_if = 0;
>  
> -			if ($c =~ /\bif\s*\(.*[^<>!=]=[^=].*/s) {
> +			if ($c =~ /\bif\s*\((.*[^<>!=]=[^=].*)\)/s) {
> +				my $expr = $1;
> +
> +				# Allow ACQUIRE_ERR() special case
> +				if ($expr =~ /\w+\s*=\s*ACQUIRE_ERR\s*\(/) {
> +					next;
> +				}
> +

Thanks! This lookls like a good fixup to send after ACQUIRE_ERR() moves
upstream.  Should probably go with a wider set to update checkpatch's
understanding of other scoped-based-macros like DEFINE_{FREE,GUARD}().