printk deadlock due to double lock attempt on current CPU's runqueue

[Sultan Alsawaf]

On Wed, Nov 10, 2021 at 11:13:37AM +0106, John Ogness wrote:
> Even after we introduce kthread printers, there will still be situations
> where direct printing is used: booting (before kthreads exist) and
> shutdown/suspend/crash situations, when the kthreads may not be
> active.

Although I'm unaware of any ongoing kthread printer work, I'm curious to know
how a kthread approach wouldn't employ a try_to_wake_up() from directly inside
printk(), since the try_to_wake_up() hit from inside the fbcon code is what
caused my deadlock.

Sultan