linux-kernel - Re: BUG: kernel crash report, odd...

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Date:	Tue, 10 Jul 2007 00:29:54 +0200
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"Charles Shannon Hendrix" <shannon@...omaker.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: BUG: kernel crash report, odd...

Forgot a few things, see below...

On 10/07/07, Jesper Juhl <jesper.juhl@...il.com> wrote:
> On 10/07/07, Charles Shannon Hendrix <shannon@...omaker.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.
>
0.5. Perhaps increase the size of the kernels log buffer (the
LOG_BUF_SHIFT config option)

> 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.
>

-- 
Jesper Juhl <jesper.juhl@...il.com>
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