linux-kernel - Re: [cpuops cmpxchg double V3 3/5] Generic support for this_cpu_cmpxchg

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Date:	Fri, 25 Feb 2011 15:28:37 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Tejun Heo <tj@...nel.org>, akpm@...ux-foundation.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [cpuops cmpxchg double V3 3/5] Generic support for
 this_cpu_cmpxchg_double

On Fri, Feb 25, 2011 at 11:38:53AM -0600, Christoph Lameter wrote:
>  
> +/*
> + * Special handling for cmpxchg_double. cmpxchg_double is passed two
> + * percpu variables. The first has to be aligned to a double word
> + * boundary and the second has to follow directly thereafter.
> + */
> +#define __pcpu_double_call_return_int(stem, pcp1, pcp2, ...)		\
> +({									\
> +	int ret__;							\
> +	__verify_pcpu_ptr(&pcp1);					\
> +	VM_BUG_ON((unsigned long)(&pcp1) % (2 * sizeof(pcp1)));		\
> +	VM_BUG_ON((unsigned long)(&pcp2) != (unsigned long)(&pcp1) + sizeof(pcp1));\
> +	VM_BUG_ON(sizeof(pcp1) != sizeof(pcp2));			\

Since this is a macro, and it looks like all these are constants (sizeof
and addresses), couldn't you just do a BUILD_BUG_ON() instead?

-- Steve


> +	switch(sizeof(pcp1)) {						\
> +	case 1: ret__ = stem##1(pcp1, pcp2, __VA_ARGS__);break;		\
> +	case 2: ret__ = stem##2(pcp1, pcp2, __VA_ARGS__);break;		\
> +	case 4: ret__ = stem##4(pcp1, pcp2, __VA_ARGS__);break;		\
> +	case 8: ret__ = stem##8(pcp1, pcp2, __VA_ARGS__);break;		\
> +	default:							\
> +		__bad_size_call_parameter();break;			\
> +	}								\
> +	ret__;								\
> +})
> +
--
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