linux-kernel - Re: percpu: Define this_cpu_cpumask_var_t

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Message-ID: <20140821222212.GA7996@mtj.dyndns.org>
Date:	Thu, 21 Aug 2014 17:22:12 -0500
From:	Tejun Heo <htejun@...il.com>
To:	Christoph Lameter <cl@...two.org>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Fengguang Wu <fengguang.wu@...el.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Motohiro Kosaki <Motohiro.Kosaki@...fujitsu.com>,
	Mike Travis <travis@....com>
Subject: Re: percpu: Define this_cpu_cpumask_var_t_ptr

Hello, Christoph.

On Thu, Aug 07, 2014 at 10:05:45AM -0500, Christoph Lameter wrote:
> @@ -666,10 +666,19 @@
>   *
>   * This code makes NR_CPUS length memcopy and brings to a memory corruption.
>   * cpumask_copy() provide safe copy functionality.
> + *
> + * Note that there is another evil here: If you define a cpumask_var_t
> + * as a percpu variable then the way to obtain the address of the cpumask
> + * structure differently influences what this_cpu_* operation needs to be
> + * used. Please use this_cpu_cpumask_var_t in those cases. The direct use
> + * of this_cpu_ptr() or this_cpu_read() will lead to failures when the
> + * other type of cpumask_var_t implementation is configured.
>   */
>  #ifdef CONFIG_CPUMASK_OFFSTACK
>  typedef struct cpumask *cpumask_var_t;
> 
> +#define this_cpu_cpumask_var_t_ptr(x) this_cpu_read(x)
> +
>  bool alloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node);
>  bool alloc_cpumask_var(cpumask_var_t *mask, gfp_t flags);
>  bool zalloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node);
> @@ -681,6 +690,8 @@
>  #else
>  typedef struct cpumask cpumask_var_t[1];
> 
> +#define this_cpu_cpumask_var_t_ptr(x) this_cpu_ptr(&x)

Urgh, this is nasty but yeah I can't think of any other way around it
either. :(

Do we need the "_t" in the name tho?  Maybe we can shorten the name to
this_cpumask_var_ptr(x)?  Also, wouldn't it be better to define it as
a static inline function so that the input type is explicit?

Thanks.

-- 
tejun
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