Subject: Re: question about preempt_disable()
From: Rob Love <rml@tech9.net>
To: Matthias Urlichs <smurf@smurf.noris.de>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <pan.2003.11.30.17.39.47.71027@smurf.noris.de>
References: <000d01c3b6dd$30ab34a0$8a04a943@bananacabana>
	 <pan.2003.11.30.17.39.47.71027@smurf.noris.de>
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Date: Sun, 30 Nov 2003 22:53:41 -0500
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Sender: linux-kernel-owner@vger.kernel.org

On Sun, 2003-11-30 at 12:39, Matthias Urlichs wrote:

> You need to prevent deadlocks. Imagine process A grabbing a spinlock, then
> getting preempted. Process B now sits there and waits on the spinlock.
> Forward progress may or may not happen when the scheduler preempts B and
> restarts A, some indeterminate time later.

Further, on uniprocessor systems, we don't have deadlocks so it is the
preempt_disable() that actually ensures concurrency is prevented in the
critical region.

	Rob Love


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