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Date: Tue, 17 Sep 2002 17:53:33 +0200 (CEST)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: Ingo Molnar <mingo@elte.hu>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: Robert Love <rml@tech9.net>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] BUG(): sched.c: Line 944
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On Tue, 17 Sep 2002, Linus Torvalds wrote:

> 	void schedule(void)
> 	{
> 		BUG_ON(in_atomic());
> 		BUG_ON(current->state & TASK_ZOMBIE);
> 		do_schedule();
> 	}
> 
> 	void exit_schedule(void)
> 	{
> 		BUG_ON(!(current->state & TASK_ZOMBIE));
> 		do_schedule();
> 	}

i'd rather do it the other way around - ie. do a:

	if (unlikely(current->state == TASK_ZOMBIE)) {
		... exit checks ...
	} else {
		... normal checks ...
	}

this test is cheaper than a function call. I'd say the ZOMBIE check alone
is not significant enough to introduce a function split in the hotpath.  
This check is also easier to remove later on.

TASK_ZOMBIE is only ever allowed to be set for exiting tasks. [and if
TASK_ZOMBIE handling is broken then it will trigger the normal atomic
tests so it's not like we are silently ignoring those errors.]

	Ingo

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