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SubjectRe: frequent lockups in 3.18rc4
On Tue, Nov 18, 2014 at 05:02:54PM -0500, Dave Jones wrote:
> On Tue, Nov 18, 2014 at 04:55:40PM -0500, Don Zickus wrote:
>
> > > So here we mangle CPU3 in and lose the backtrace for cpu0, which might
> > > be the real interesting one ....
> >
> > Can you provide another dump? The hope is we get something not mangled?
>
> Working on it..
>
> > The other option we have done in RHEL is panic the system and let kdump
> > capture the memory. Then we can analyze the vmcore for the stack trace
> > cpu0 stored in memory to get a rough idea where it might be if the cpu
> > isn't responding very well.
>
> I don't know if it's because of the debug options I typically run with,
> or that I'm perpetually cursed, but I've never managed to get kdump to
> do anything useful. (The last time I tried it was actively harmful in
> that not only did it fail to dump anything, it wedged the machine so
> it didn't reboot after panic).
>
> Unless there's some magic step missing from the documentation at
> http://fedoraproject.org/wiki/How_to_use_kdump_to_debug_kernel_crashes
> then I'm not optimistic it'll be useful.

Well, I don't know when the last time you ran it, but I know the RH kexec
folks have started pursuing a Fedora-first package patch rule a couple of
years ago to ensure Fedora had a working kexec/kdump solution.

As for the wedging part, it was a common problem to have the kernel hang
while trying to boot the second kernel (and before console output
happened). So the problem makes sense and is unfortunate. I would
encourage you to try again. :-)

Though, it is transitioning to have the app built into the kernel to deal
with the whole secure boot thing, so that might be another can of worms.

I cc'd Vivek and he can let us know how well it works with F21.

Cheers,
Don


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