From owner-freebsd-hackers  Sun Jun 23 13:19:38 2002
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Date: Sun, 23 Jun 2002 13:19:33 -0700
From: Alfred Perlstein <bright@mu.org>
To: Matthew Dillon <dillon@apollo.backplane.com>
Cc: freebsd-hackers@freebsd.org,
	Julian Elischer <julian@elischer.org>, Alan Cox <alc@cs.rice.edu>,
	Tor.Egge@cvsup.no.freebsd.org
Subject: Re: Bug in wakeup() (stable and current) ?
Message-ID: <20020623201933.GM53232@elvis.mu.org>
References: <200206232014.g5NKE5x3058562@apollo.backplane.com>
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* Matthew Dillon <dillon@apollo.backplane.com> [020623 13:14] wrote:
>     This doesn't look right at all.  It looks like wakeup is not restarting
>     properly:
> 
>         s = splhigh();
>         qp = &slpque[LOOKUP(ident)];
> restart:
>         TAILQ_FOREACH(p, qp, p_procq) {
>                 if (p->p_wchan == ident) {
>                         TAILQ_REMOVE(qp, p, p_procq);
>                         p->p_wchan = 0;
>                         if (p->p_stat == SSLEEP) {
> 				...
> 				goto restart;
> 			}
> 			/* XXXXXX goto restart should occur HERE XXXXXX */
> 		}
> 	}
> 
>     The goto restart condition should occur one level up, as I show in
>     the comment.
> 
>     Could someone take a look at this and tell me if I am blowing smoke?

I'm pretty sure you only need to 'goto restart' if you call into
maybe_resched() as someone else may have manipulated the queues.

The 'restart' label is only in there for restarting in case one of
the functions called may change the lists, if we restart _every_
time we'll traverse the same procs where p->p_wchan != ident over
and over needlessly.

-Alfred

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