On 2021-11-10, Daniel Vetter daniel@ffwll.ch wrote:
I'm a bit out of the loop but from lwn articles my understanding is that part of upstreaming from -rt we no longer have the explicit "I'm a safe console for direct printing" opt-in. Which I get from a backwards compat pov, but I still think for at least fbcon we really should never attempt a direct printk con->write, it's just all around terrible.
Right now we don't have an explicit "I'm a safe console for direct printing" option. Right now all printing is direct. But it sounds to me that we should add this console flag when we introduce kthread printers.
So yeah for fbcon at least I think we really should throw out direct con->write from printk completely.
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.
I will introduce a console flag so that consoles can opt-out for direct printing. (opt-out rather than opt-in is probably easier, since there are only a few that would need to opt-out).
Since kthread printers do not yet exist (hoping to get them in for 5.17), I am not sure how we should address the reported bug for existing kernels.
John Ogness