linux-kernel - Re: [RFC] arm: Add for atomic half word exchange

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Message-ID: <20150519121349.GE2067@n2100.arm.linux.org.uk>
Date:	Tue, 19 May 2015 13:13:49 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Sarbojit Ganguly <ganguly.s@...sung.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"Waiman.Long@...com" <Waiman.Long@...com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"vikram.m@...sung.com" <vikram.m@...sung.com>,
	"raghavendra.kt@...ux.vnet.ibm.com" 
	<raghavendra.kt@...ux.vnet.ibm.com>,
	"oleg@...hat.com" <oleg@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	SHARAN ALLUR <sharan.allur@...sung.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>
Subject: Re: [RFC] arm: Add for atomic half word exchange

On Tue, May 19, 2015 at 11:20:11AM +0000, Sarbojit Ganguly wrote:
> Yes, I will try to do that. OTOH, I saw that  there was a discussion on
> removal of bad_xchg() altogether. Perhaps that approach be better than
> adding this half word exchange?

The only possibility for removal of __bad_xchg() is to remove it's
_definition_ only, not its callsite, so that we get a _link_ time
error for use cases we don't support.

Removing its callsite leaves us open to code malfunction: xchg()
effectively becomes a no-op for sizes which are not supported, and
that's a _very_ bad thing to happen.

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