Unable to handle kernel NULL pointer dereference (was Re: Unofficial Squeeze installer image available)

[Richard Mortimer <richm@oldelvet.org.uk>]

Hi,

One of the other issues that I spotted just cropped up again. After a 
quick check I don't see a similar bug report and will report one later 
unless anyone knows of one here.

I get the following fatal ooops just before setting up the network in 
the installer during netboot.

[  225.950970] Unable to handle kernel NULL pointer dereference
[  226.025376] tsk->{mm,active_mm}->context = 0000000000000588
[  226.098688] tsk->{mm,active_mm}->pgd = fffff800ddb9c000
[  226.167644] Kernel panic - not syncing: Aiee, killing interrupt handler!
[  226.256067] Press Stop-A (L1-A) to return to the boot prom

I've actually reproduced it a few times. Unfortunately it is proving 
difficult to get the full Oops stack trace out of it because klogd is 
altering the /proc/sys/kernel/printk console log level and is stopping 
getting the information to the console.

I've managed to change the logging level by booting using BOOT_DEBUG=3 
and applying the changes below but that seems to change the timing and 
the problem doesn't occur. If you are able to rebuild the netboot image with

/sbin/klogd -c 7

in /lib/debian-installer-startup.d/S10syslog (normally it uses -c 2)

then that would mean that I could test it without having to use BOOT_DEBUG=3

Procedure for booting and manually tweaking S10syslog is as follows:

boot using

boot net BOOT_DEBUG=3

then use "exit" to leave the "just booted" debug shell

then in the "before init" debug shell run the following

cat > /lib/debian-installer-startup.d/S10syslog <<EOF
echo -n "Starting system log daemon: "
/sbin/syslogd -m 0 -O /var/log/syslog -S
echo -n "syslogd, "
/sbin/klogd -c 7
echo "klogd."
EOF
exit

I then reply with "English" as language and "United Kingdom". The crash 
happens for me shortly after this point but before it starts mentioning 
network cards.


Regards

Richard