linux-kernel - Re: [RFC][PATCH 3/3] locking,arm64: Introduce cmpwait()

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Date:	Mon, 4 Apr 2016 15:12:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	linux-kernel@...r.kernel.org, will.deacon@....com
Cc:	waiman.long@....com, mingo@...hat.com, paulmck@...ux.vnet.ibm.com,
	boqun.feng@...il.com, torvalds@...ux-foundation.org,
	dave@...olabs.net
Subject: Re: [RFC][PATCH 3/3] locking,arm64: Introduce cmpwait()

On Mon, Apr 04, 2016 at 02:22:53PM +0200, Peter Zijlstra wrote:
> +#define __CMPWAIT_GEN(w, sz, name)					\

 +static inline  \

> +void __cmpwait_case_##name(volatile void *ptr, unsigned long val)	\
> +{									\
> +	unsigned long tmp;						\
> +									\
> +	asm volatile(							\
> +	"	ldxr" #sz "\t%" #w "[tmp], %[v]\n"			\
> +	"	eor	%" #w "[tmp], %" #w "[tmp], %" #w "[val]\n"	\
> +	"	cbnz	%" #w "[tmp], 1f\n"				\
> +	"	wfe\n"							\
> +	"1:"								\
> +	: [tmp] "=&r" (tmp), [val] "=&r" (val),				\
> +	  [v] "+Q" (*(unsigned long *)ptr));				\

And this probably wants a "memory" clobber to force reload values after
this returns.

> +}