bug#26706: mingetty consumes 40% CPU printing the login prompt over and over

[myglc2 <myglc2@gmail.com>]

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I noticed that my headless server running GuixSD was busy when I am not
doing anything. When I looked at top I saw mingetty consuming 40% CPU
...

$ top -o %CPU -n 1 | head -n 25
top - 20:44:13 up 5 days, 12:58,  3 users,  load average: 0.33, 0.33, 0.35
Tasks: 192 total,   1 running, 191 sleeping,   0 stopped,   0 zombie
%Cpu0  :   0.0/0.1     0[                                                                  ]
%Cpu1  :   0.1/2.9     3[||                                                                ]
%Cpu2  :   0.2/4.0     4[|||                                                               ]
%Cpu3  :   0.3/4.9     5[|||                                                               ]
%Cpu4  :   0.2/0.1     0[                                                                  ]
%Cpu5  :   0.2/4.6     5[|||                                                               ]
%Cpu6  :   0.2/4.3     5[|||                                                               ]
%Cpu7  :   0.3/4.1     4[|||                                                               ]
GiB Mem :  6.5/15.610   [                                                                  ]
GiB Swap:  0.0/9.649    [                                                                  ]

  PID USER      PR  NI    VIRT    RES  %CPU %MEM     TIME+ S COMMAND
  384 root      20   0    6.2m   0.3m  40.0  0.0   2386:36 S mingetty
    7 root      20   0    0.0m   0.0m   6.7  0.0   2:20.86 S rcu_sched
 4154 g1        20   0  300.3m 135.1m   6.7  0.8   3:37.67 S emacs
 7431 root      20   0    0.0m   0.0m   6.7  0.0   0:26.07 S kworker/u16:2
 7539 root      20   0    0.0m   0.0m   6.7  0.0   0:06.54 S kworker/u16:0
    1 root      20   0  130.1m  27.9m   0.0  0.2   0:03.22 S shepherd

If I plug in a console display, I see the login prompt is being rapidly
printed over and over. If I hit the console return key the printing
stops and mingetty stops using CPU.

I am running a relatively recent GuixSD built from git checkout ...

g1@g1 ~$ guix --version
guix (GNU Guix) 0.12.0
g1@g1 ~$ stat ~/.config/guix/latest | grep File:
  File: /home/g1/.config/guix/latest -> /home/g1/src/guix/
g1@g1 ~$ git -C ~/.config/guix/latest describe
v0.12.0-3191-g25a49294c
g1@g1 ~$ git -C ~/.config/guix/latest log -n 1 --oneline
25a49294c cache: Work around 'time-monotonic' bug in Guile 2.2.2.

Here is the system config:


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;;; GuixSD headless server
(use-modules (gnu))
(use-service-modules networking ssh)
(use-package-modules
 base disk admin linux qemu screen
 ssh certs xorg cups
 freeipmi rsync wget version-control)
(operating-system
  (host-name "g1")
  (timezone "America/New_York")
  (locale "en_US.utf8")
  (kernel-arguments '("console=ttyS1,115200"))
  ;; RAID1 root using 1 NVMe SSD + 2 HDs
  (bootloader (grub-configuration (device "/dev/nvme0n1")))
  (initrd (lambda (file-systems . rest) (apply base-initrd file-systems
					       #:extra-modules '("raid1")
					       rest)))
  (mapped-devices (list (mapped-device
			 (source '("/dev/nvme0n1p1" "/dev/sda1" "/dev/sdb1"))
			 (target "/dev/md3")
			 (type raid-device-mapping))))
  (file-systems (cons (file-system
			(title 'device)
			(device "/dev/md3")
			(mount-point "/")
			(type "ext4")
			(dependencies mapped-devices))
		      %base-file-systems))
  (swap-devices '("/dev/nvme0n1p2" ))
  (users (cons* (user-account (name "g1")
			      (group "users")
			      (supplementary-groups '("wheel" "kvm"))
			      (home-directory (string-append "/home/" name)))
		(user-account (name "admin")
			      (group "users")
			      (supplementary-groups '("wheel" "kvm"))
			      (home-directory (string-append "/home/" name)))
		%base-user-accounts))
  (packages (cons*
	     cups
	     freeipmi
	     git
	     glibc-utf8-locales
	     gnu-make
	     mdadm
	     nss-certs
	     openssh
	     parted
	     qemu
	     rsync
	     screen
	     smartmontools
	     wget
	     xauth
	     %base-packages))
  (services (cons* (dhcp-client-service)
		   (ntp-service)
		   (service openssh-service-type (openssh-configuration
						  (x11-forwarding? #t)))
		   (agetty-service (agetty-configuration (tty "ttyS1")
							 (baud-rate "115200")))
		   %base-services)))