Re: use of preempt_count instead of in_atomic() at leds-gpio.c

From: Andrew Morton <akpm@linux-foundation.org>
To: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: David Brownell <david-b@pacbell.net>,
	Richard Purdie <rpurdie@rpsys.net>,
	linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>
Subject: Re: use of preempt_count instead of in_atomic() at leds-gpio.c
Date: Thu, 20 Mar 2008 16:47:41 -0700	[thread overview]
Message-ID: <20080320164741.734e838c.akpm@linux-foundation.org> (raw)
In-Reply-To: <20080320225612.GB20788@khazad-dum.debian.net>

On Thu, 20 Mar 2008 19:56:12 -0300 Henrique de Moraes Holschuh <hmh@hmh.eng.br> wrote:

> Can we add "in_scheduleable()", or maybe "can_schedule()", that returns
> in_atomic() if CONFIG_PREEMT, or 0 if there is no way to know?   To my
> limited knowledge of how that part of the kernel works, it would do the
> right thing.

If we did that, then people would use it.  And that would be bad.  It'll
lead to code which behaves differently on non-preemptible kernels, to code
which works less well on non-preemptible kernels and it will lead to less
well-thought-out code in general.

Really, this all points at an ill-designed part of the leds interface.  The
consistent pattern we use in the kernel is that callers keep track of
whether they are running in a schedulable context and, if necessary, they
will inform callees about that.  Callees don't work it out for themselves.