Date: Tue, 16 Jul 2002 16:13:32 -0400 (EDT) From: John Baldwin <jhb@FreeBSD.org> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: current@FreeBSD.org Subject: Re: VOP_GETATTR panic on Alpha Message-ID: <XFMail.20020716161332.jhb@FreeBSD.org> In-Reply-To: <15668.31168.555993.138907@grasshopper.cs.duke.edu>
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On 16-Jul-2002 Andrew Gallatin wrote:
>
> John Baldwin writes:
> > >
> > > So its still stuck in msleep. How is it supposed to get back to
> > > the panic'ed thread if a system thread wakes up and is not allowed to
> > > go back to sleep???
> >
> > Hmmmmm. Surprised we don't see this on other archs then (or maybe
> > we do...). Probably when we have panic'd (and after we leave the
> > debugger and go into boot() or some such) we should take any non-P_SYSTEM
> > processes off the run queues and then remove the panicstr checks from
> > msleep() and the condition variable wait functions.
>
> Do you have something like the following psuedo code in mind?
> Perhaps placed just prior to the call to boot() in panic()?
>
> foreach p in (all procs in system) {
> if (p == curproc)
> continue
> if (p->p_flag & P_SYSTEM)
> continue;
> foreach td in (all threads in p)
> if (td->td_state == TDS_RUNQ)
> remrunqueue(td);
> }
>
> I assume a panic will IPI other processors and halt them in their
> tracks so we don't need to worry too much about locking?
Hmm, it doesn't atm. Debugger() does, but panic doesn't.
> > Perhaps better is to dink around in choosethread() so that if panicstr
> > is set, we throw away any threads get that aren't P_SYSTEM or have the
> > TDF_INPANIC flag set. By throw away, I mean that we just ignore any such
> > threads and loop if we get one we want to throw away.
>
> I think that I like your first idea better..
I like my second, it is easier, just add this to choosethread:
if (panicstr &&
((td->td_proc->p_flag & P_SYSTEM) == 0 &&
(td->td_flags & TDF_INPANIC) == 0))
goto top;
(Do this just before the td_state change and return()).
You of couse need to set TDF_INPANIC when setting panicstr. This
might mean that we break the restartable panics case. In that
case you would just change this so that runq_choose() actually does
the work to ignore threads on the run queue instead which eliminates
the loop and ugly goto and preserves the runqueue state in the core
dump.
> Drew
--
John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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