linux-kernel - Re: [PATCH locking/atomic 18/19] locking/atomic: Refrain from generating duplicate fallback kernel-doc

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Message-ID: <20230511193856.GA2296992@hirez.programming.kicks-ass.net>
Date:   Thu, 11 May 2023 21:38:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        linux-kernel@...r.kernel.org, x86@...nel.org, akiyks@...il.com,
        linux-doc@...r.kernel.org, kernel-team@...a.com,
        Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH locking/atomic 18/19] locking/atomic: Refrain from
 generating duplicate fallback kernel-doc

On Thu, May 11, 2023 at 06:10:00PM +0100, Mark Rutland wrote:
> Hi Paul
> 
> On Wed, May 10, 2023 at 11:17:16AM -0700, Paul E. McKenney wrote:
> > The gen-atomics.sh script currently generates 42 duplicate definitions:
> > 
> > 	arch_atomic64_add_negative
> > 	arch_atomic64_add_negative_acquire
> > 	arch_atomic64_add_negative_release
> 
> 	[...]
> 
> > These duplicates are presumably to handle different architectures
> > generating hand-coded definitions for different subsets of the atomic
> > operations.
> 
> Yup, for each FULL/ACQUIRE/RELEASE/RELAXED variant of each op, we allow the
> archtiecture to choose between:
> 
> * Providing the ordering variant directly
> * Providing the FULL ordering variant only
> * Providing the RELAXED ordering variant only
> * Providing an equivalent op that we can build from
> 
> > However, generating duplicate kernel-doc headers is undesirable.
> 
> Understood -- I hadn't understood that duplication was a problem when this was
> originally written.
> 
> The way this is currently done is largely an artifact of our ifdeffery (and the
> kerneldoc for fallbacks living inthe fallback templates), and I think we can
> fix both of those.
> 
> > Therefore, generate only the first kernel-doc definition in a group
> > of duplicates.  A comment indicates the name of the function and the
> > fallback script that generated it.
> 
> I'm not keen on this approach, especially with the chkdup.sh script -- it feels
> like we're working around an underlying structural issue.
> 
> I think that we can restructure the ifdeffery so that each ordering variant
> gets its own ifdeffery, and then we could place the kerneldoc immediately above
> that, e.g.
> 
> 	/**
> 	 * arch_atomic_inc_return_release()
> 	 *
> 	 * [ full kerneldoc block here ]
> 	 */
> 	#if defined(arch_atomic_inc_return_release)
> 	/* defined in arch code */
> 	#elif defined(arch_atomic_inc_return_relaxed)
> 	[ define in terms of arch_atomic_inc_return_relaxed ]
> 	#elif defined(arch_atomic_inc_return)
> 	[ define in terms of arch_atomic_inc_return ]
> 	#else
> 	[ define in terms of arch_atomic_fetch_inc_release ]
> 	#endif
> 
> ... with similar for the mandatory ops that each arch must provide, e.g.
> 
> 	/**
> 	 * arch_atomic_or()
> 	 *
> 	 * [ full kerneldoc block here ]
> 	 */
> 	/* arch_atomic_or() is mandatory -- architectures must define it! */
> 
> I had a go at that restructuring today, and while local build testing indicates
> I haven't got it quite right, I think it's possible:
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=atomics/fallback-rework
> 
> Does that sound ok to you?

If the end result is simpler scripts, sure.

I'm not at all keen to complicate the scripts for something daft like
kernel-doc. The last thing we need is documentation style weenies making
an unholy mess of things.