Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

[Sergey Senozhatsky]

On (01/15/18 09:51), Petr Mladek wrote:
> On Sat 2018-01-13 16:31:00, Sergey Senozhatsky wrote:
> > On (01/12/18 13:55), Petr Mladek wrote:
> > [..]
> > > > I'm not fixing console_unlock(), I'm fixing printk(). BTW, all my
> > > > kernels are CONFIG_PREEMPT (I'm a RT guy), my mind thinks more about
> > > > PREEMPT kernels than !PREEMPT ones.
> > > 
> > > I would say that the patch improves also console_unlock() but only in
> > > non-preemttive context.
> > > 
> > > By other words, it makes console_unlock() finite in preemptible context
> > > (limited by buffer size). It might still be unlimited in
> > > non-preemtible context.
> > 
> > could you elaborate a bit?
> 
> Ah, I am sorry, I swapped the conditions. I meant that
> console_unlock() is finite in non-preemptible context.

by the way. just for the record,

probably there is a way for us to have a task printing more than
O(logbuf) even in non-preemptible context.

	CPU0

	vprintk_emit()
	 preempt_disable()
	  console_unlock()
	  {
	   for (;;) {
                printk_safe_enter_irqsave()
	        call_console_drivers();
	        printk_safe_exit_irqrestore()

	<< IRQ >>
		dump_stack()
		 printk()->log_store()
		 ....
		 printk()->log_store()
	<< iret >>
	   }
	  }
	 preempt_enable()

	-ss