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

Sergey Senozhatsky
2018-01-16T05:16:28Z

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