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** Changed in: linux (Ubuntu)
Status: New => Incomplete
** Tags added: bionic
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https://bugs.launchpad.net/bugs/1807140
Title:
The last console= argument is not used by the kernel
Status in linux package in Ubuntu:
Incomplete
Bug description:
I ran into a problem with the console argument handling on a physical
system with a BMC (Dell R610) and also reproduced the same behavior on
a QEMU/KVM VM with multiple serial ports.
The kernel documentation notes that the last entry will be used for
/dev/console
https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-tty
"What: /sys/class/tty/console/active
Shows the list of currently configured console devices, like 'tty1
ttyS0'. The last entry in the file is the active device connected to
/dev/console.
The file supports poll() to detect virtual console switches."
https://elixir.bootlin.com/linux/v4.15.18/source/kernel/printk/printk.c#L1960
"The last preferred console added will be used for kernel messages and
stdin/out/err for init."
The actual behavior is different and the console specified in the last
console argument does not become an active one. As a result, SOL
functionality is not possible to use unless only one ttyS<n> argument
is specified in the kernel command line arguments. Setting the
arguments to only contain the right one results in a proper behavior
and I can see rx counters increasing in /proc/tty/driver/serial for
the relevant port after I type something via the BMC.
$ cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-4.15.0-42-generic
root=UUID=580a3c58-1040-4c7d-b94f-93230874caf5 ro console=tty0
console=ttyS0,115200 console=ttyS1,115200
journalctl -k | grep ttyS
Dec 03 21:42:41 ubuntu kernel: Command line:
BOOT_IMAGE=/vmlinuz-4.15.0-42-generic
root=UUID=580a3c58-1040-4c7d-b94f-93230874caf5 ro console=tty0
console=ttyS0,115200 console=ttyS1,115200
Dec 03 21:42:41 ubuntu kernel: Kernel command line:
BOOT_IMAGE=/vmlinuz-4.15.0-42-generic
root=UUID=580a3c58-1040-4c7d-b94f-93230874caf5 ro console=tty0
console=ttyS0,115200 console=ttyS1,115200
Dec 03 21:42:41 ubuntu kernel: console [ttyS0] enabled
Dec 03 21:42:41 ubuntu kernel: 00:02: ttyS0 at I/O 0x3f8 (irq = 4, base_baud
= 115200) is a 16550A
Dec 03 21:42:41 ubuntu kernel: 00:03: ttyS1 at I/O 0x2f8 (irq = 3, base_baud
= 115200) is a 16550A
Dec 03 21:42:41 ubuntu kernel: tty ttyS3: hash matches
Full dmesg: http://paste.ubuntu.com/p/bV2pDc4Hdw/
$ cat /sys/class/tty/console/active
ttyS0 tty0
$ sudo cat /proc/tty/driver/serial
serinfo:1.0 driver revision:
0: uart:16550A port:000003F8 irq:4 tx:78 rx:0 RTS|DTR
1: uart:16550A port:000002F8 irq:3 tx:0 rx:0 CTS|DSR|CD
2: uart:unknown port:000003E8 irq:4
3: uart:unknown port:000002E8 irq:3
# ...
~~~
GRUB setttings:
# the ones that override /etc/default/grub
$ cat /etc/default/grub.d/50-curtin-settings.cfg
cat: cat: No such file or directory
GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,115200
console=ttyS1,115200"
# disable grub os prober that might find other OS installs.
GRUB_DISABLE_OS_PROBER=true
GRUB_TERMINAL=console
/etc/default/grub: https://paste.ubuntu.com/p/sdWQrY7JwN/
# grub.cfg: http://paste.ubuntu.com/p/zKGTqDh6sR/
# two entries, both with the proper arg and properly sent to the kernel
cmdline based on /proc/cmdline
grep ttyS grub.cfg
linux /vmlinuz-4.15.0-42-generic
root=UUID=580a3c58-1040-4c7d-b94f-93230874caf5 ro console=tty0
console=ttyS0,115200 console=ttyS1,115200
linux /vmlinuz-4.15.0-42-generic
root=UUID=580a3c58-1040-4c7d-b94f-93230874caf5 ro console=tty0
console=ttyS0,115200 console=ttyS1,115200
~~~
I managed to reproduce the exact same behavior on a VM with multiple
8250 serial ports.
ubuntu@maas-vhost5:~$ cat /sys/class/tty/console/active
ttyS0
ubuntu@maas-vhost5:~$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-4.15.0-42-generic
root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS0,115200
console=ttyS2,115200 console=ttyS1,115200
ubuntu@maas-vhost5:~$ grep -RP ttyS /boot/grub/grub.cfg
linux /boot/vmlinuz-4.15.0-42-generic
root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS0,115200
console=ttyS2,115200 console=ttyS1,115200
linux /boot/vmlinuz-4.15.0-42-generic
root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS0,115200
console=ttyS2,115200 console=ttyS1,115200
linux /boot/vmlinuz-4.15.0-39-generic
root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS0,115200
console=ttyS2,115200 console=ttyS1,115200
# changed to the following config with only ttyS1 present:
ubuntu@maas-vhost5:~$ grep -RP ttyS /boot/grub/grub.cfg
linux /boot/vmlinuz-4.15.0-42-generic
root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS1,115200
linux /boot/vmlinuz-4.15.0-42-generic
root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS1,115200
linux /boot/vmlinuz-4.15.0-39-generic
root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS1,115200
# 1 tty passed only
ubuntu@maas-vhost5:~$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-4.15.0-42-generic
root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS1,115200
# now it's shown as active
ubuntu@maas-vhost5:~$ cat /sys/class/tty/console/active
ttyS1
ubuntu@maas-vhost5:~$ sudo cat /proc/tty/driver/serial
serinfo:1.0 driver revision:
0: uart:16550A port:000003F8 irq:4 tx:0 rx:0 CTS|DSR|CD
1: uart:16550A port:000002F8 irq:3 tx:14763 rx:0 RTS|CTS|DTR|DSR|CD
2: uart:16550A port:000003E8 irq:4 tx:0 rx:0 CTS|DSR|CD
~~~~
Relevant code:
https://elixir.bootlin.com/linux/v4.15.18/source/kernel/printk/printk.c#L2379
https://elixir.bootlin.com/linux/v4.15.18/source/kernel/printk/printk.c#L1916
https://elixir.bootlin.com/linux/v4.15.18/source/kernel/printk/printk.c#L1961
https://elixir.bootlin.com/linux/v4.15.18/source/kernel/printk/printk.c#L1886
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