linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Wed, 19 Nov 2014 09:41:05 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Dave Jones <davej@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>, vgoyal@...hat.com
Subject: Re: 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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