Re: How to get backtrace? modprobe -r iwlagn; modprobe iwlagn kills kernel

Re: How to get backtrace? modprobe -r iwlagn; modprobe iwlagn kills kernel

[Milton Miller]

On Wed May 18 2011 about 10:37:54 EST, Stevie Trujillo wrote:
> I'm having some problem getting a backtrace. When I do "modprobe -r
> iwlagn; modprobe iwlagn" (2.6.38.6 with Intel-1030N) the kernel crashes
> (sometimes I need to try 2 or 3 times, and sometimes the modprobe -r
> is the one that crashes).
> 
> This spams my monitor with several oops/panics before it finally
> dies. I can only see bottom of the last one, which probably isn't
> very meaningful.  I tried loading netconsole, but I only get one or
> two lines before it stops sending/printing.
> 
> I then tried kexec+crashkernel, but I only managed to get a backtrace
> for the last panic (which I think is just a result of memory corruption
> or something).  Finally I tried compiling ramoops into my kernel,
> but it didn't want to load because of "No such device".

For the kexec+crashkernel, try to retrieve the kernel log buffer:

There are some macros available, but basically log_buf is a pointer
to a buffer of length log_buf_len initialized to __log_buf (but can
be expanded via the command line or sysctl, in). log_end is the
end of the buffer.  If you haven't wrapped then just print log_end
characters.

Also consider setting /proc/sys/kernel/panic_on_oops to 1 to
concentrate on the first one.  It won't help getting the oops to your
syslog but maybe it will keep it on the screen.

Hope this helps,
milton

Re: How to get backtrace? modprobe -r iwlagn; modprobe iwlagn kills kernel

[Américo Wang]

On Wed, May 18, 2011 at 11:55 PM, Milton Miller <miltonm@bga.com> wrote:
> On Wed May 18 2011 about 10:37:54 EST, Stevie Trujillo wrote:
>> I'm having some problem getting a backtrace. When I do "modprobe -r
>> iwlagn; modprobe iwlagn" (2.6.38.6 with Intel-1030N) the kernel crashes
>> (sometimes I need to try 2 or 3 times, and sometimes the modprobe -r
>> is the one that crashes).
>>
>> This spams my monitor with several oops/panics before it finally
>> dies. I can only see bottom of the last one, which probably isn't
>> very meaningful.  I tried loading netconsole, but I only get one or
>> two lines before it stops sending/printing.
>>
>> I then tried kexec+crashkernel, but I only managed to get a backtrace
>> for the last panic (which I think is just a result of memory corruption
>> or something).  Finally I tried compiling ramoops into my kernel,
>> but it didn't want to load because of "No such device".
>
> For the kexec+crashkernel, try to retrieve the kernel log buffer:
>

There is a utility in kexec-tools, named vmcore-dmesg, which
is supposed to do this kind of thing.