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

[Petr Mladek]

On Tue 2018-01-16 14:16:22, Sergey Senozhatsky wrote:
> 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()

Great catch! And good to know about it when designing further
improvements.

Best Regards,
Petr