Date: Fri, 20 Feb 2004 19:25:17 +1100 From: Tim Robbins <tjr@freebsd.org> To: Mike Makonnen <mtm@identd.net> Cc: freebsd-threads@FreeBSD.org Subject: Re: libthr patch Message-ID: <20040220082517.GA42604@cat.robbins.dropbear.id.au> In-Reply-To: <20040220073830.GB1089@mobile.acs-et.com> References: <20040219062850.GC1074@mobile.acs-et.com> <20040219134733.GA38023@cat.robbins.dropbear.id.au> <20040220073830.GB1089@mobile.acs-et.com>
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On Fri, Feb 20, 2004 at 10:38:30AM +0300, Mike Makonnen wrote:
> On Fri, Feb 20, 2004 at 12:47:33AM +1100, Tim Robbins wrote:
> > On Thu, Feb 19, 2004 at 09:28:50AM +0300, Mike Makonnen wrote:
> >
> > Make sure you fix thr_wake() to check that uap->id is valid before you
> > commit this patch. Something like this would be safer but slower:
>
> Hmm, you're right. I should've thought of that. Thanks for catching it.
>
> >
> > struct thread *td1;
> >
> > PROC_LOCK(td->td_proc);
> > FOREACH_THREAD_IN_PROC(td->td_proc, td1)
> > if (td1 == (struct thread *)uap->id)
> > break;
> > if (td1 == NULL) {
> > PROC_UNLOCK(td->td_proc);
> > return (ESRCH);
> > }
> > td1->td_lthrflags |= LTF_THRWAKEUP;
> > wakeup_one(td1);
> > PROC_UNLOCK(td->td_proc);
> > return (0);
> >
> > (I'm not sure that it's safe to call wakeup_one() on a thread pointer
> > that isn't curthread without holding the proc lock, so I changed that too.)
>
> Sorry, I don't follow. How can a thread call wakeup_one() on itself (if it's
> supposed to be asleep)?
>
> A cursory look through the call path doesn't show anything that needs a
> proc lock. There is access to p->p_state but either sched_lock or proc lock
> is sufficient for that (and the accessing function does hold sched_lock).
What I mean is: I don't know whether you can be sure that the thread hasn't
already been freed between the time unlock the proc and when you call
wakeup_one(). I assumed the list of threads associated with a process was
protected by the proc lock.
Tim
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