Re: [RFC PATCH v1 00/25] printk: new implementation

[Sergey Senozhatsky]

On (02/12/19 15:29), John Ogness wrote:
> - console_flush_on_panic() currently is a NOP. It is pretty clear how
>   this could be implemented if atomic_write was available. But if no
>   such console is registered, it is not clear what should be done. Is
>   this function really even needed?

If you now rely on a fully preemptible printk kthread to flush
pending logbuf messages, then console_flush_on_panic() is your
only chance to see those pending logbuf messages on the serial
console when the system dies.

Non-atomic consoles should become atomic once you call bust_spinlocks(1),
this is what we currently have:

	panic()
	bust_spinlocks(1)                       // sets oops_in_progress
	console_flush_on_panic()
	 call_console_drivers()
	  -> serial_driver_write()
	      if (oops_in_progress)
	        locked = spin_trylock_irqsave(&port->lock);
	      uart_console_write();
	      if (locked)
	        spin_unlock_irqrestore(&port->lock);

	-ss