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    SubjectRe: BUG: kernel crash report, odd...
    On Tue, 10 Jul 2007 00:29:54 +0200 Jesper Juhl wrote:

    > Forgot a few things, see below...
    >
    > On 10/07/07, Jesper Juhl <jesper.juhl@gmail.com> wrote:
    > > On 10/07/07, Charles Shannon Hendrix <shannon@widomaker.com> wrote:
    > > >
    > > > A system I was using a few minutes ago dumped this to the syslog:
    > > >
    > > > Jul 9 17:50:38 daydream kernel: [76022.613000] BUG: unable to handle
    > > > kernel NUL
    > > > L pointer dereference at virtual address 00000010
    > > > Jul 9 17:50:38 daydream kernel: [76022.613000] printing eip:
    > > > Jul 9 17:50:38 daydream kernel: [76022.613000] c01ace66
    > > > Jul 9 17:50:38 daydream kernel: [76022.613000] *pde = 00000000
    > > > Jul 9 17:50:38 daydream kernel: [76022.613000] Oops: 0000 [#1]
    > > >
    > > >
    > > > There was no other information either before or after.
    > > >
    > > > What I saw was my KDE desktop stopped responding to events.
    > > >
    > > > Machine didn't respond to power switch.
    > > >
    > > > Unfortunately, that's all I know.
    > > >
    > > > In the past when I had bugs like this, I got a fairly extensive kernel
    > > > error message, but this time the above is the only thing I saw.
    > > >
    > > It does look a little short... probably the rest just didn't make it to disk...
    > >
    > > > I have not had kernel bugs like this until I started running 2.6.20 on a
    > > > new Kubuntu install.
    > > >
    > > > Same hardware, but Slackware and my own custom 2.6.19 kernel never
    > > > crashed.
    > > >
    > > Different kernel source version, different configuration, probably
    > > different compiler, Slackware doesn't patch the vanilla kernel - I
    > > believe (k)ubuntu does. All in all that equals a significantly
    > > different kernel binary you have been running in those two cases.
    > >
    > A different userspace could also be the cause. In theory, userspace
    > should never be able to crash the kernel, but in real life bugs happen
    > and sometimes userspace manages to cause a kernel crash. So, a
    > different userspace environment in your new distribution could in
    > theory expose a bug that didn't surface with your previous
    > distribution.
    >
    > > > Is there anything I can do, in case this happens again, to try and
    > > > capture more information?
    > > >
    > > 0. Make sure the kernels loglevel is set so that you get all messages.

    i.e., boot with "ignore_loglevel"

    > 0.5. Perhaps increase the size of the kernels log buffer (the
    > LOG_BUF_SHIFT config option)

    or boot with "log_buf_len=n[KMG]" (power of 2 required)

    > > 1. Make sure syslog is setup to capture all kernel messages, both
    > > errors, warnings, notices, debug messages etc.
    > >
    > > 2. If you can, check output of 'dmesg' instead of just what made it to syslog.
    > >
    > > 3. If you have a second PC, setup serial console or netconsole to
    > > capture kernel messages on that second box. This can sometimes capture
    > > messages that don't make it to disk.
    > >
    > > 4. Build a custom kernel with some (or all) of the debug options under
    > > the Kernel Hacking menu enabled.
    > >
    > > 5. Even when the system hangs you may in some cases be able to get
    > > some info (or just sync the disks and do a reboot) via magic sysrq.

    ---
    ~Randy
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