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Date: Wed, 10 Jul 2002 20:31:03 +0200 (CEST)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: Ingo Molnar <mingo@elte.hu>
To: Erich Focht <efocht@ess.nec.de>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       linux-ia64 <linux-ia64@linuxia64.org>
Subject: Re: O(1) scheduler "complex" macros
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On Tue, 9 Jul 2002, Erich Focht wrote:

> Suppose we have 
>   cpu1: idle1
>   cpu2: prev2 -> next2  (in the switch)
> 
> I don't understand how task_lock(prev2) done on cpu2 can prevent cpu1 to
> schedule prev2, which it stole after the RQ#2 lock release. It will just
> try to task_lock(idle1), which will be successfull.

you are right - the 'complex' macros also need to lock the 'next' task,
not only the 'previous' task - but to do that deadlock-free, they need to
drop the runqueue lock ...

	Ingo

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