On Mon, 2007-02-12 at 14:16 +0100, Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
> > Jan Kiszka wrote:
> > 
> >>2.6.19 didn't magically start to work as well. Instead I have a back
> >>trace now, see attachment.
> >>
> >>I included a full set of 16k points, but the thrilling things are around
> >>-73 to -25: Some Linux process with IRQs on gets preempted by an RT-IRQ
> >>(RTnet NIC). That triggers an RT kernel thread to run for a while (RTnet
> >>stack manager, prio 98). But when returning to Linux again, its IRQs
> >>remain masked now. The reason must be that weird exception at -62. Don't
> >>know where it comes from and why is there no report about THAT issue in
> >>the kernel logs.
> > 
> > 
> > The cause of this page fault will get tracked down later today, but the
> > way it is handled already causes some doubts to me. To make discussion
> > easier, here is the relevant excerpt from the trace:
> Maybe this fault is due to the No-cow patch ? Before the no-cow patch,
> vmalloced areas were added to all processes page directories, now they
> are added only to the page directories of processes with the VM_PINNED
> flag. So, if ipipe_test_root tries to access some module memory area
> over the context of a non-realtime thread, a fault will occur.

Yes, it's a minor fault occurring due to on-demand memory mapping, this
is why we don't get any alarming message in the kernel log.


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