linux-kernel - RE: [PATCH 2/5] arm64: add __READ_ONCE

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Message-ID: <c2bee816a4a44d55951ca839fea0a6dd@AcuMS.aculab.com>
Date: Sat, 9 Nov 2024 09:49:03 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Haris Okanovic' <harisokn@...zon.com>, "ankur.a.arora@...cle.com"
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Subject: RE: [PATCH 2/5] arm64: add __READ_ONCE_EX()

From: Haris Okanovic
> Sent: 05 November 2024 18:31
> 
> Perform an exclusive load, which atomically loads a word and arms the
> exclusive monitor to enable wfet()/wfe() accelerated polling.
> 
...
> +	atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(__x))__x);\

That doesn't do what you want it to do.
(It is wrong in READ_ONCE() as well.)

?: is treated like an arithmetic operator and the result will get
promoted to 'int'.
Moving the first cast outside the ?: probably works:
	(typeof(*__x))(atomic ? __u.__val : (*(volatile typeof(__x))__x));

   David

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