linux-kernel - Re: use of preempt_count instead of in

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Date:	Mon, 24 Mar 2008 12:42:29 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	corbet@....net (Jonathan Corbet)
Cc:	stern@...land.harvard.edu, khali@...ux-fr.org, mb@...sch.de,
	hmh@....eng.br, david-b@...bell.net, rpurdie@...ys.net,
	linux-kernel@...r.kernel.org, mingo@...e.hu, geert@...ux-m68k.org
Subject: Re: use of preempt_count instead of in_atomic() at leds-gpio.c

On Mon, 24 Mar 2008 13:34:49 -0600
corbet@....net (Jonathan Corbet) wrote:

> Discourage people from using in_atomic()
> 
> Signed-off-by: Jonathan Corbet <corbet@....net>
> 
> diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
> index 4982998..3d196cb 100644
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -72,6 +72,11 @@
>  #define in_softirq()		(softirq_count())
>  #define in_interrupt()		(irq_count())
>  
> +/*
> + * Are we running in atomic context?  WARNING: this macro cannot
> + * always detect atomic context and should not be used to determine
> + * whether sleeping is possible.  Do not use it in driver code.
> + */
>  #define in_atomic()		((preempt_count() & ~PREEMPT_ACTIVE) != 0)

It'd be better if the comment were to describe _why_ in_atomic() is
unreliable.  ie: "does not account for held spinlocks on non-preemptible
kernels".

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