linux-kernel - Re: [PATCH v2 1/8] cleanup: Introduce ACQUIRE() and ACQUIRE

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Message-ID: <68547e76d1dc_1f8d1008f@dwillia2-xfh.jf.intel.com.notmuch>
Date: Thu, 19 Jun 2025 14:17:42 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Dan Williams <dan.j.williams@...el.com>, <linux-cxl@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Linus Torvalds
	<torvalds@...ux-foundation.org>, David Lechner <dlechner@...libre.com>,
	"Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>
Subject: Re: [PATCH v2 1/8] cleanup: Introduce ACQUIRE() and ACQUIRE_ERR()
 for conditional locks

Dan Williams wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> 
> scoped_cond_guard(), automatic cleanup for conditional locks, has a couple
> pain points:
> 
> * It causes existing straight-line code to be re-indented into a new
>   bracketed scope. While this can be mitigated by a new helper function
>   to contain the scope, that is not always a comfortable conversion.
> 
> * The return code from the conditional lock is tossed in favor of a scheme
>   to pass a 'return err;' statement to the macro.
> 
> Other attempts to clean this up, to behave more like guard() [1], got hung
> up trying to both establish and evaluate the conditional lock in one
> statement.
> 
> ACQUIRE() solves this by reflecting the result of the condition in the
> automatic variable established by the lock CLASS(). The result is
> separately retrieved with the ACQUIRE_ERR() helper, effectively a PTR_ERR()
> operation.
> 
> Link: http://lore.kernel.org/all/Z1LBnX9TpZLR5Dkf@gmail.com [1]
> Link: http://patch.msgid.link/20250512105026.GP4439@noisy.programming.kicks-ass.net
> Link: http://patch.msgid.link/20250512185817.GA1808@noisy.programming.kicks-ass.net
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: David Lechner <dlechner@...libre.com>
> Cc: Fabio M. De Francesco <fabio.m.de.francesco@...ux.intel.com>
> Not-yet-signed-off-by: Peter Zijlstra <peterz@...radead.org>
> [djbw: wrap Peter's proposal with changelog and comments]
> Co-developed-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

With Peter's sign-off, pushed to for-6.17/cleanup-acquire as a stable
commit that others can reference:

https://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl.git/log/?h=for-6.17/cleanup-acquire