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Date:   Fri, 15 Mar 2019 13:15:41 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Thomas =?iso-8859-1?Q?M=FCller?= <thomas@mathtm.de>
Cc:     linux-kernel@vger.kernel.org
Subject: Re: disabling secondary CPU hangs / system fails to suspend with
 kernel 4.19+
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On Fri, Mar 15, 2019 at 12:41:00PM +0100, Thomas M?ller wrote:

> > What .config do you have?
> The one packaged by Fedora. I've attached the one for 4.20.15 as reference.

Thanks, I'll have a poke, see what, if anything, is different from the
kernels I ran.

> > And what, if anything do you see on the
> > console when it goes funny?
> Nothing unfortunately.
> When trying to suspend the display immediately goes blank, the system becomes unresponsive and the
> status LED within the power button start flashing rapidly (just like it does when the power cord is
> attached).
> 
> 
> > I think you wrote that hot-un-plug never completes? Is there anything in
> > dmesg when it's stuck in:
> > 
> >   echo 0 > /sys/devices/system/cpu/cpu1/online
> > 
> > ?
> I've just tried that again and the system immediately froze.

Hmm, I tought you said the system remained semi usable, just that reboot
stopped working thereafter and it needed a power cycle.

> `journalctl -f` was running in a second window but it had no chance to output anything... :/

Ah, you're using a GUI!

Stop doing that ;-)

See if you can use the VGA console; not a FB console or a DRM console,
but the real ancient, proper text mode, VGA console.

Now, don't ask me how to do that, because I don't know, I've been
running on pure serial console output for the past 10 years or so, heck
I don't even have systemd.

And you might have to do something like: dmesg -n8, to get the console
to print the kernel messages or something.