The kernel’s printk()
function seems like it should be relatively simple; all it does is format a
string and output it to the kernel logs. That simplicity hides a lot of
underlying complexity, though, and that complexity is why kernel developers
are still unhappy with printk() after 28 years. At the 2019 Linux
Plumbers Conference, John Ogness explained
where the complexity in printk() comes from and what is being done
to improve the situation.

Source: LWN.net – [$] Why printk() is so complicated (and how to fix it)