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

[<dan.j.williams@intel.com>]

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}().