On Sat, Oct 04, 2014 at 06:26:33PM +0800, GP Orcullo wrote:
> On Sat, Oct 4, 2014 at 6:48 AM, Gilles Chanteperdrix
> <[email protected]> wrote:
> > On Sat, Oct 04, 2014 at 06:45:08AM +0800, GP Orcullo wrote:
> >> On Sat, Oct 4, 2014 at 3:14 AM, Gilles Chanteperdrix
> >> <[email protected]> wrote:
> >> > On Fri, Oct 03, 2014 at 11:28:52PM +0800, GP Orcullo wrote:
> >> >> I've added BUG_ON(!hard_irqs_disabled()) to the code and got the
> >> >> kernel to oops at startup.
> >> >>
> >> >> Where shall I start looking for the offending code?
> >> >
> >> > The thing is, all the tracepoints you have are late after the
> >> > fault. A better strategy is to replace BUG_ON(!hard_irqs_disabled)
> >> > with:
> >> >
> >> > if (!hard_irqs_disabled()) {
> >> > ipipe_trace_panic_freeze();
> >> > ipipe_trace_panic_dump();
> >> > BUG();
> >> > }
> >> >
> >>
> >> The results are almost similar.
> >>
> >
> >> [ 15.550769] Unable to handle kernel NULL pointer dereference at virtual
> >> address 0000000c
> >
>
> This is due to user error - I've mixed up the module versions...
>
> > This is not caused by the code above. This is another bug.
> >
> > With the code above, you should see a line
> > "BUG" or something.
> >
>
> Getting this kernel to print any messages before lockup is very
> difficult. Is there another way of debugging it beside using jtag?
>
I generally use printk or the I-pipe tracer in some creative way
(trigger a trace freeze on some condition then BUG()). You could for
instance check whether the Linux timer irq is still running by
putting a printascii(".") there every HZ ticks. If it is not running
check the same with the Xenomai timer irq, then finally the I-pipe
timer ack function. On x86 we have the NMI watchdog to help with
lockups, maybe someone could implement a similar functionality with
FIQ on ARM.
--
Gilles.
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