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Date: Fri, 30 Aug 2002 01:12:38 -0700
From: Andrew Morton <akpm@zip.com.au>
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To: Ingo Molnar <mingo@elte.hu>
CC: Linus Torvalds <torvalds@transmeta.com>, linux-kernel@vger.kernel.org
Subject: Re: [patch] scheduler fixes, 2.5.32-BK
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Ingo Molnar wrote:
> 
> >  - changes the migration code to use struct completion. Andrew pointed out
> >    that there might be a small window in where the up() touches the
> >    semaphore while the waiting task goes on and frees its stack. And
> >    completion is more suited for this kind of stuff anyway.
> 
> actually, i think the race does not exist. up() is perfectly safely done
> on the on-stack semaphore, because both the wake_up() done by __up() and
> the __down() path takes the waitqueue spinlock, so i cannot see where the
> up() touches the semaphore after the down()-ed task has been woken up.
> 

yep, looks like the killing of the semaphore_lock made the race
go away.

But ia64, sparc and x86_64 use semaphore_lock, so they still are
exposed.