linux-kernel - Intel laptop: Starting with `maxcpus=1` and then bringing other CPUs online freezes system

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Message-ID: <125e904a-088e-f111-00a4-95c3b18d882f@molgen.mpg.de>
Date:   Thu, 11 Jun 2020 10:59:01 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Mario Limonciello <mario.limonciello@...l.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Christian Kellner <ckellner@...hat.com>,
        linux-pm@...r.kernel.org
Subject: Intel laptop: Starting with `maxcpus=1` and then bringing other CPUs
 online freezes system

Dear Linux folks,

This is an interesting one. On a Dell Precision 3540 with a dedicated 
AMD graphics card, and with Debian Sid/unstable and Linux 5.6.14, there 
are several strange issues (one example [1]).

Starting the system, and adding `maxcpus=1` to the Linux command line, 
the system starts.

Trying to bring up more CPUs, works for the first one, but fails for the 
second. The system freezes then. Nothing is dumped on the Linux virtual 
terminal.

In my limited tests, this always happens, when the system runs on 
batteries, that means, without the power cord plugged in. But I was also 
able to reproduce it with the USB Type-C power cable plugged in. But 
sometimes it works (to bring all other seven CPUs online).

Please find the Linux messages up to bringing CPU 1 online attached with 
no power cord plugged in, and the messages of a successful operation.

Is this expected? I’d appreciated tips, if it’s possible to debug this 
further.

Kind regards,

Paul

[1]: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1883065

View attachment "linux-5.6.14-dmesg-maxcpus1-on-battery-up-to-2nd-cpu.txt" of type "text/plain" (87285 bytes)

View attachment "linux-5.6.14-dmesg-maxcpus1-with-charger-all-cpus-online.txt" of type "text/plain" (88200 bytes)