Virtualization with KVM-Qemu triggers kernel log debug message flood
kode54
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Joined: 19 Nov 2017
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It appears that 4.13.13-1 has the following enabled:

CONFIG_DEBUG_PREEMPT=y
CONFIG_DEBUG_BUGVERBOSE=y
CONFIG_DEBUG_KERNEL=y

And due to the mix of preempt and some KVM bug, it floods my kernel with this mess:

termbin.com/6cvp

A bit from someone in #qemu:

<peterx> kode54, I am not an expert, but I think that's because kvm_vcpu_block() called single_task_running() without disabling preemption (while you enabled DEBUG_PREEMPT in kernel so you see that warning). I think we may need some kvm expert to know better

Can I safely disable some of these things, until such time as I need to actually debug my kernel?

EDIT: Holy crap, you enable the following, too:

CONFIG_MAGIC_SYSRQ=y
CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x1
CONFIG_MAGIC_SYSRQ_SERIAL=y
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techAdmin
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Location: East Coast, West Coast? I know it's one of them.
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Just as an aside, the primary purpose of liquorix is to be a highly optimized desktop kernel, not a server kernel. That doesn't alter your issue validity, but it's worth keeping in mind the purpose of liquorix.
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kode54
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One of the VMs I'm running is my primary desktop OS. It's a little weird.
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techAdmin
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well, damentz is the man, so I'm sure he'll take a good look at the issue. Meanwhile, if you post:

inxi -bxx

that might give him some useful system data to work with.
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kode54
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:: Code ::
System:    Host: umaro Kernel: 4.13.13-1-lqx x86_64 bits: 64 gcc: 7.2.0
           Console: tty 1 dm: sddm,sddm Distro: Arch Linux
Machine:   Device: desktop Mobo: MSI model: Z77A-GD65 (MS-7751) v: 2.0 serial: N/A
           UEFI: American Megatrends v: V10.11 date: 10/09/2013
CPU:       Quad core Intel Core i7-3770 (-HT-MCP-) arch: Ivy Bridge rev.9
           speed/max: 1900/3401 MHz
Graphics:  Card-1: Intel Xeon E3-1200 v2/3rd Gen Core processor Graphics Controller
           bus-ID: 00:02.0 chip-ID: 8086:0162
           Card-2: Advanced Micro Devices [AMD/ATI] Ellesmere [Radeon RX 470/480/570/580]
           bus-ID: 01:00.0 chip-ID: 1002:67df
           Display Server: X.org 1.19.5 drivers: modesetting (unloaded: vesa)
           tty size: 80x24 Advanced Data: N/A for root out of X
Network:   Card: Intel 82579V Gigabit Network Connection
           driver: e1000e v: 3.2.6-k port: f080
           bus-ID: 00:19.0 chip-ID: 8086:1503
Drives:    HDD Total Size: 14258.8GB (1.2% used)
Info:      Processes: 240 Uptime: 2:24 Memory: 27815.4/32119.2MB
           Init: systemd v: 235 Gcc sys: 7.2.0
           Client: Shell (bash 4.4.121 running in tty 1) inxi: 2.3.43

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damentz
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Joined: 09 Sep 2008
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Hi kode54,

I'll look into disabling that debugging output. Some of those options like "CONFIG_DEBUG_KERNEL" are required for options that tools like powertop use, CONFIG_DEBUG_PREEMPT might be similar.

On the other hand, I don't know what CONFIG_DEBUG_BUGVERBOSE is for, so I'll do some research and see what can be disabled safely.

As for the magic sysrq's, they're still useful for gracefully recovering from system hang, so I won't be turning them off.
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kode54
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Joined: 19 Nov 2017
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If DEBUG_PREEMPT is required for some tool, perhaps I should be running my virtual machines under a non-preempt kernel instead. Maybe Liquorix isn't right for me.

I just know that DEBUG_PREEMPT plus KVM-Qemu results in 2GB per day of kernel logs.
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damentz
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Can you try the latest version? DEBUG_PREEMPT is off plus many of remaining debug settings.
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kode54
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Joined: 19 Nov 2017
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Just FYI, you didn't include "-lqx" as a version suffix in this new configuration. Has that been dropped?

EDIT: Weird, it was something that showed up in my config diff, but it appeared in the build anyway. Eh, I guess it's nothing to worry about. Will test tonight.
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