BUG: kernel crash report, odd...

BUG: kernel crash report, odd...

[Charles Shannon Hendrix]

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.

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.

Is there anything I can do, in case this happens again, to try and
capture more information?

-- 
shannon           | An Irishman is never drunk as long as he can hold onto 
                  | one blade of grass and not fall off the face of the earth.

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

[Jesper Juhl]

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.

> 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.

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@gmail.com>
Don't top-post  http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please      http://www.expita.com/nomime.html

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

[Jesper Juhl]

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.
>
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@gmail.com>
Don't top-post  http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please      http://www.expita.com/nomime.html

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

[Randy Dunlap]

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
*** Remember to use Documentation/SubmitChecklist when testing your code ***

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

[Hugh Dickins]

On Mon, 9 Jul 2007, Charles Shannon Hendrix 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 NULL 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.

Something simple you can do, which I didn't see mentioned yet:
look up the entries before and after c01ace66 in that 2.6.20
kernel's System.map, then post the output of
objdump -d --start-address=0xbefore --stop-address=0xafter vmlinux
so people here can see the function name and the oopsing instruction
in its context.  May not help at all, but well worth trying.

Hugh