On 10/12/07, Daniel Rossier <[EMAIL PROTECTED]> wrote:
> Philippe Gerum wrote:
> > On Thu, 2007-10-11 at 18:35 +0200, ROSSIER Daniel wrote:
> > > Hi everyone,
> > >
> > > I'm taking over the original thread from Patrick concerning the
> > > port of Xenomai on Xscale with Linux 2.6.20. Briefly summarized,
> > > the boot process actually freezes after a while right after the
> > > nucleus has been started.
> > >
> > > I've investigated the issue over the last hours, and I came up with
> > > the following conclusion: it seems that the problem is due to a
> > > endless loop in do_gettimeofday in arch/arm/kernel/time.c. Here is
> > > the code:
> > >
> > > "... do { seq = read_seqbegin_irqsave(&xtime_lock, flags); usec =
> > > system_timer->offset(); sec = xtime.tv_sec; usec += xtime.tv_nsec /
> > > 1000; } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
> > > ..."
> > >
> > > If I remove the do { } while loop with the call to
> > > read_seqbegin_irqsave(), then the boot process is going ahead (I
> > > got a suspicious error like "I-pipe: Detected illicit call from
> > > domain 'Xenomai' " but it might well be normal with such a
> > > modification.
> > >
> > > I checked with the code from a 2.6.15 kernel, and it is basically
> > > the same structure.
> > >
> > > Any idea about the cause of this problem?
> > >
> >
> > That's typical of someone from the real-time (Xenomai) domain
> > spuriously calling into this routine, which is illegal.
> >
> > The usual scenario for the lockup to happen is: - Linux task A calls
> > into some code grabbing the xtime lock for writing - Xenomai preempts
> > task A before it releases the seqlock, e.g. to process an interrupt -
> > some code on behalf of the Xenomai IRQ handler calls into
> > do_gettimeofday, which is wrong - the culprit gets a reader lock
> > sequence token, which will never match the quiescent state. This will
> > cause an infinite loop, since task A can't get out the critical
> > section to put the sequence in a quiescent state again, until the
> > Xenomai code relinquishes the CPU. Catch #22.
> >
> > You likely need to chase the code who triggers the "Detected illicit
> > domain" message, likely in some code also calling do_gettimeofday().
> >
>
> Ok I'll do it. What I find weird is that the the do_gettimeofday() is
> called by xnpod_start_timer(kernel/xenomai/nucleus/pod.c). It is
xnpod_start_timer is called at module initialization time or by
threads running in secondary mode, so, calling do_gettimeofday should
not cause any problem. xnpod_start_timer documentation states this
very clearly.
--
Gilles Chanteperdrix
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