From owner-cvs-src@FreeBSD.ORG  Wed Jun  9 09:33:08 2004
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From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Wed, 09 Jun 2004 09:29:08 -0000."
             <200406090929.i599T8h6065944@repoman.freebsd.org> 
Date: Wed, 09 Jun 2004 11:33:05 +0200
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cc: cvs-src@FreeBSD.org
cc: src-committers@FreeBSD.org
cc: cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/sys/kern kern_proc.c 
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In message <200406090929.i599T8h6065944@repoman.freebsd.org>, Poul-Henning Kamp
 writes:
>
>  Modified files:
>    sys/kern             kern_proc.c 
>  Log:
>  Fix a race in destruction of sessions.

Not to pick on anybody, but this is a perfect example of getting locking
almost right:

BAD:

	LOCK(foo->lock)
	foo->refcount--;
	UNLOCK(foo->lock)
	if (foo->refcount == 0)
		destroy(foo);

GOOD:

	LOCK(foo->lock)
	i = --foo->refcount;
	UNLOCK(foo->lock)
	if (i == 0)
		destroy(foo);


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.