linux-kernel - Re: [PATCH -v2 19/33] locking,powerpc: Implement atomic{,64}_fetch_{add,sub,and,or,xor}{,_relaxed,_acquire,

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Message-ID: <20160601031138.GA30064@insomnia>
Date:	Wed, 1 Jun 2016 11:11:38 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	torvalds@...ux-foundation.org, mingo@...nel.org,
	tglx@...utronix.de, will.deacon@....com,
	paulmck@...ux.vnet.ibm.com, waiman.long@....com,
	fweisbec@...il.com, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, rth@...ddle.net, vgupta@...opsys.com,
	linux@....linux.org.uk, egtvedt@...fundet.no, realmz6@...il.com,
	ysato@...rs.sourceforge.jp, rkuo@...eaurora.org,
	tony.luck@...el.com, geert@...ux-m68k.org, james.hogan@...tec.com,
	ralf@...ux-mips.org, dhowells@...hat.com, jejb@...isc-linux.org,
	mpe@...erman.id.au, schwidefsky@...ibm.com, dalias@...c.org,
	davem@...emloft.net, cmetcalf@...lanox.com, jcmvbkbc@...il.com,
	arnd@...db.de, dbueso@...e.de, fengguang.wu@...el.com
Subject: Re: [PATCH -v2 19/33] locking,powerpc: Implement
 atomic{,64}_fetch_{add,sub,and,or,xor}{,_relaxed,_acquire,_release}()

Hi Peter,

On Tue, May 31, 2016 at 12:19:44PM +0200, Peter Zijlstra wrote:
[snip]
>  
> @@ -329,20 +361,53 @@ atomic64_##op##_return_relaxed(long a, a
>  	return t;							\
>  }
>  
> +#define ATOMIC64_FETCH_OP_RELAXED(op, asm_op)				\
> +static inline long							\
> +atomic64_fetch_##op##_relaxed(long a, atomic64_t *v)			\
> +{									\
> +	long res, t;							\
> +									\
> +	__asm__ __volatile__(						\
> +"1:	ldarx	%0,0,%4		# atomic64_fetch_" #op "_relaxed\n"	\
> +	#asm_op " %1,%3,%0\n"						\
> +"	stdcx.	%1,0,%4\n"						\
> +"	bne-	1b\n"							\
> +	: "=&r" (res), "=&r" (t), "+m" (v->counter)			\
> +	: "r" (a), "r" (&v->counter)					\
> +	: "cc");							\
> +									\
> +	return t;							\

Looks like I missed this one in v1, it should be
	
	return res;

because the primitives will return the values before modified by the
operations.

Regards,
Boqun

> +}
> +

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