Enabling DDB prevent kernel from panicing

[nickolasbug at gmail.com]

Hello, Mark

2011/1/11 Mark Saad <nonesuch at longcount.org>:
> All
> This was originally posted to hackers@
>
> I have a good question that I cant find an answer for. I believe
> found a kernel bug in 7.3-RELEASE that prevents me from booting 64-bit
> kernels on HP's DL360 G4p . The kernel dies with "Fatal trap 12: page
> fault while in kernel mode " . The hardware works fine in 7.2-RELEASE
> amd64, 7.1-RELEASE amd64, and 6.4-RELEASE amd64 .
>
> In 7.3-RELEASE amd64 I can not boot from cd or pxe correctly using the
> stock 7.3-RELEASE amd64 kernel however i386 works fine. To see if this
> issue was some how fixed in 7.3-RELEASE-p4 amd64 I rebuilt a GENERIC
> kernel using patches sources and tried to boot and I got the same
> crash.
>
>  Next I rebuilt the kernel with KDB and DDB to see if I could get a
> core-dump of the system. I also set loader.conf to
>
> kernel="kernel.DEBUG"
> kern.dumpdev="/dev/da0s1b"
>
> Next I pxebooted  the box and the system does not crash on boot up, it
> will easily load a nfs root and work fine. So I copied my debug
> kernel, and loader.conf to the local disk and rebooted and it boots
> fine from the local disk .

Looks like a race condition.
Well, you don't need to compile KDB and DDB, just add

makeoptions DEBUG=-g

into your kernel config file and rebuild kernel.

Then after you got a crash dump you can easy debug it (see FreeBSD
Developers Handbok):
http://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug-gdb.html


wbr,
Nickolas