[BUG] Deadlock in Fiasco kernel

Frank Mehnert fm3 at os.inf.tu-dresden.de
Tue Mar 6 08:47:39 CET 2007

Hi Daniel,

On Tuesday 06 March 2007, Daniel Vandersee wrote:
> I noticed that the Fiasco kernel hangs under some circumstances so the
> whole system stops working. Unfortunately I wasn't even able to enter
> the kernel debugger via a serial cable in this case. The error is
> reproducible on different plattforms (e.g. Thinkpad T43, 1GB RAM,
> Pentium M 1.8 GHz or Thinkpad T41) even though it only appears from time
> to time (probability ~50% or even better). Within VMWare or Qemu this
> deadlock does *not* appear. Furthermore this error does not occur if the
> kernel was started using the "-esc" option. I wasn't able to reproduce
> this bug on a HP nx7400 (Dual Core T2300, 1GB RAM).
> We use an own dynamic loader to load some L4 tasks whereas other L4
> tasks, as the mGUI, are loaded by GRUB.
> The bug can be reproduced on real hardware using the iso-image which I
> will upload to the SLOX server (deadlock.iso). You have to choose GRUB
> entry two or three. If the error occurs the system hangs in text mode
> otherwise a graphical mode is entered. Sometimes you have to reboot up
> to 20 times but it usually occurs immediately.

To debug such issues the builtin watchdog is very helpful. Make sure that
CONFIG_WATCHDOG is enabled in the kernel configuration and pass the
-watchdog parameter at the kernel command line. A builtin Local APIC is
required. If the kernel deadlocks for some reason and the interrupts are
disabled, the watchdog will force the CPU to enter the Fiasco kernel

Kind regards,

## Dept. of Computer Science, Dresden University of Technology, Germany ##
## http://os.inf.tu-dresden.de/~fm3                                     ##
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