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Subject: Re: Patch: linux-2.5.8-pre1/kernel/exit.c change caused BUG() at
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From: Robert Love <rml@tech9.net>
To: Andrew Morton <akpm@zip.com.au>
Cc: Roger Larsson <roger.larsson@norran.net>,
        Linus Torvalds <torvalds@transmeta.com>,
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On Thu, 2002-04-04 at 17:38, Andrew Morton wrote:

> With the appropriate locking, memory barriers and other
> relevant goo I think this would work...

Yah, I guess, but that isn't pretty at all ;)

Andrew, remember how we used to do it (and still do it in the 2.4
patch)?  Wouldn't that work?  Specifically, when we enter
preempt_schedule we set a flag value in preempt_count.  This flag value
is checked at the top of schedule and, if set, we skip the first chunk
of code that handles sleeping tasks.  The task->state never changes. 
Upon leaving schedule and returning to preempt_schedule, we unset the
flag.

This allows us to preempt tasks in any state, without problems or
special cases.  It also wasn't too much overhead - compared to now,
basically just:

	if (unlikely(current->preempt_count() & PREEMPT_ACTIVE))
		goto pick_next_task;

at the top of schedule().

	Robert Love

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