Re: frequent lockups in 3.18rc4

From: Vivek Goyal
Date: Wed Nov 19 2014 - 10:03:45 EST

On Wed, Nov 19, 2014 at 09:41:05AM -0500, Don Zickus wrote:
> 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).

Hi Dave Jones,

Not being able to capture the dump I can understand but having wedged
the machine so that it does not reboot after dump failure sounds bad.
So you could not get machine to boot even after a power cycle? Would
you remember what was failing. I am curious to know what did kdump do
to make machine unbootable.

> >
> > Unless there's some magic step missing from the documentation at
> >
> > then I'm not optimistic it'll be useful.

I had a quick look at it and it basically looks fine. In fedora ideally
it is just two steps process.

- Reserve memory using crashkernel. Say crashkernel=160M
- systemctl start kdump
- Crash the system or wait for it to crash.

So despite your bad experience in the past, I would encourage you to
give it a try.

> 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.

Yep, now we are putting everything in fedora first so it should be much
better. Hard to say the same thing about driver authors. Sometimes they
might have a driver working in rhel and not necessarily upstream. I am
not sure if you ran into one of those issues.

Also recently I have seen issues with graphics drivers too.

> 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 doubt that secureboot bits will contribute to the failure.

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