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Date: Wed, 9 Jun 2004 18:28:57 +0200 (CEST)
From: Lukas Ertl <le@FreeBSD.org>
To: Poul-Henning Kamp <phk@phk.freebsd.dk>
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cc: "M. Warner Losh" <imp@bsdimp.com>
Subject: Re: cvs commit: src/sys/kern kern_proc.c 
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On Wed, 9 Jun 2004, Poul-Henning Kamp wrote:

> Assume foo->refcount = 2;
>
> 	thread1 (low priority)	thread2 (high priority)
> 	----------------------	-----------------------
>
> 	...			...
> 	LOCK(foo->lock)		...
> 	i = --foo->refcount;	LOCK(foo->lock)
> 	# i == 1, refcount == 1
> 	UNLOCK(foo->lock)
> 				i = --foo->refcount;
> 				# i == 0, refcount == 0
> 				UNLOCK(foo->lock)
> 				if (i == 0) # true
> 					destroy(foo)
> 				...
>
> 	if (i == 0) # false
> 		destroy(foo)

Is there a possibility that foo->refcount is incremented after both of 
them left the critical section, so that i is 0, but foo->refcount isn't?

cheers,
le

-- 
Lukas Ertl                         http://homepage.univie.ac.at/l.ertl/
le@FreeBSD.org                     http://people.freebsd.org/~le/