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

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Date:	Thu, 20 Mar 2008 16:47:41 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	David Brownell <david-b@...bell.net>,
	Richard Purdie <rpurdie@...ys.net>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: use of preempt_count instead of in_atomic() at leds-gpio.c

On Thu, 20 Mar 2008 19:56:12 -0300 Henrique de Moraes Holschuh <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.

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