[PATCH printk v5 1/1] printk: extend console_lock for per-console locking

[John Ogness]

On 2022-04-29, Marek Szyprowski <m.szyprowski at samsung.com> wrote:
> The same issue happens if I boot with init=/bin/bash

Very interesting. Since you are seeing all the output up until you try
doing something, I guess receiving UART data is triggering the issue.

> I found something really interesting. When lockup happens, I'm still
> able to log via ssh and trigger any magic sysrq action via
> /proc/sysrq-trigger.

If you boot the system and directly login via ssh (without sending any
data via serial), can you trigger printk output on the UART? For
example, with:

    echo hello > /dev/kmsg

(You might need to increase your loglevel to see it.)

> It turned out that the UART console is somehow blocked, but it
> receives and buffers all the input. For example after issuing "echo
>  >/proc/sysrq-trigger" from the ssh console, the UART console has been 
> updated and I see the magic sysrq banner and then all the commands I 
> blindly typed in the UART console! However this doesn't unblock the
> console.

sysrq falls back to direct printing. This would imply that the kthread
printer is somehow unable to print.

> Here is the output of 't' magic sys request:
>
> https://pastebin.com/fjbRuy4f

It looks like the call trace for the printing kthread (pr/ttyAML0) is
corrupt.

Could you post your kernel config?

John