linux-kernel - Re: [PATCH 1/7] cleanup: Introduce DEFINE_ACQUIRE() a CLASS() for conditional locking

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Message-ID: <20250512182559.GB25891@noisy.programming.kicks-ass.net>
Date: Mon, 12 May 2025 20:25:59 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: dan.j.williams@...el.com
Cc: linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Lechner <dlechner@...libre.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Fabio M. De Francesco" <fabio.maria.de.francesco@...ux.intel.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Alison Schofield <alison.schofield@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH 1/7] cleanup: Introduce DEFINE_ACQUIRE() a CLASS() for
 conditional locking

On Mon, May 12, 2025 at 12:50:26PM +0200, Peter Zijlstra wrote:

> +#define __GUARD_ERR(_ptr) \
> +	({ long _rc = (__force unsigned long)(_ptr); \
> +	   if (!_rc) { _rc = -EBUSY; } if (!IS_ERR_VALUE(_rc)) { _rc = 0; } \
> +	   _rc; })
> +

>  #define DEFINE_GUARD(_name, _type, _lock, _unlock) \
> -	DEFINE_CLASS(_name, _type, if (_T) { _unlock; }, ({ _lock; _T; }), _type _T); \
> +	DEFINE_CLASS(_name, _type, if (!__GUARD_ERR(_T)) { _unlock; }, ({ _lock; _T; }), _type _T); \
>  	DEFINE_CLASS_IS_GUARD(_name)

GCC is 'stupid' and this generates atrocious code. I'll play with it.