linux-kernel - Re: [PATCH v3 1/8] cleanup: Introduce ACQUIRE() and ACQUIRE

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Message-ID: <20250715163440.00007849@huawei.com>
Date: Tue, 15 Jul 2025 16:34:40 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Dan Williams <dan.j.williams@...el.com>
CC: <linux-cxl@...r.kernel.org>, <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 v3 1/8] cleanup: Introduce ACQUIRE() and ACQUIRE_ERR()
 for conditional locks

On Fri, 11 Jul 2025 16:49:25 -0700
Dan Williams <dan.j.williams@...el.com> 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>
> Signed-off-by: "Peter Zijlstra (Intel)" <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>

LGTM and is definitely an improvement on all previous attempts to solve this.

Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>