Re: [RFC][PATCH 2/4] res_counter check usage under val

[Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

KAMEZAWA Hiroyuki wrote:
> Add an interface to check usage is below "val"
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> 
>  include/linux/res_counter.h |   13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> Index: mmtom-stamp-2008-07-15-15-39/include/linux/res_counter.h
> ===================================================================
> --- mmtom-stamp-2008-07-15-15-39.orig/include/linux/res_counter.h
> +++ mmtom-stamp-2008-07-15-15-39/include/linux/res_counter.h
> @@ -191,4 +191,17 @@ static inline int res_counter_set_limit(
>  	return ret;
>  }
>  
> +static inline int res_counter_check_under_val(struct res_counter *cnt,
> +	unsigned long long val)
> +{
> +	unsigned long flags;
> +	int ret = 0;
> +
> +	spin_lock_irqsave(&cnt->flags, flags);

Is this spilock protection *really* required? As far as I see
from its usage it is racy itself wrt to res_counter update, so 
this locking looks superfluous.

> +	if (cnt->usage < val)
> +		ret = 1;
> +	spin_unlock_irqrestore(&cnt->flags, flags);
> +	return ret;
> +}
> +
>  #endif
> 
>