svn commit: r222537 - in head/sys: kern sys

[Garrett Cooper]

On Tue, May 31, 2011 at 2:00 PM,  <mdf at freebsd.org> wrote:
> On Tue, May 31, 2011 at 10:29 AM, Kenneth D. Merry <ken at freebsd.org> wrote:
>> Author: ken
>> Date: Tue May 31 17:29:58 2011
>> New Revision: 222537
>> URL: http://svn.freebsd.org/changeset/base/222537
>>
>> Log:
>>  Fix apparent garbage in the message buffer.
>>
>>  While we have had a fix in place (options PRINTF_BUFR_SIZE=128) to fix
>>  scrambled console output, the message buffer and syslog were still getting
>>  log messages one character at a time.  While all of the characters still
>>  made it into the log (courtesy of atomic operations), they were often
>>  interleaved when there were multiple threads writing to the buffer at the
>>  same time.
>
> This seems to panic my box with "lock "msgbuf" 0xfffffe0127ffffe0
> already initialized".
>
> Unfortunately, though I booted with a fresh CURRENT this morning
> successfully, both /boot/kernel and /boot/kernel.old give this panic.
> To add insult to injury, when the kernel drops into the debugger, my
> keyboard input no longer works so I can't get a stack, etc.
>
> So:
>
> 1) Is there anything else I can do to help debug this?

1. sysctl debug.debugger_on_panic=1 ?

> 2) how can I resurrect this box without a reinstall?

2. Best way is to probably to use the bsdinstall CD, use the LiveCD
mode, setup the system as usual (mount /, mount devfs, chroot, mount
-a), rewind to an earlier version of svn (shouldn't be too hard if you
run /etc/rc.d/network restart from inside the chroot), rebuild the
kernel (and potentially world), and install the kernel to the chroot,
then exit and reboot (this is a method I picked up from installing
Gentoo Linux multiple times, but it should work for FreeBSD as well).

This is part of the reason why I'm an avid using of make installkernel
INSTKERNNAME=$KERNCONF.$SVN_REVISION , symlink /boot/kernel to the
latest one I want to boot, and I only go through every once in a blue
moon to reap the kernels I don't need anymore -- I don't know until
after a few weeks soak on my workstation whether or not a regression
is present in the kernel.

> I will try to repro on a virtual machine so I have a snapshot to come back to.

HTH!
-Garrett