Re: [PATCH printk 11/18] printk: Convert console_drivers list to hlist

[Helge Deller]

On 9/30/22 16:20, Petr Mladek wrote:
> On Sat 2022-09-24 02:10:47, John Ogness wrote:
> > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> >
> > Replace the open coded single linked list with a hlist so a conversion to
> > SRCU protected list walks can reuse the existing primitives.
> >
> > --- a/arch/parisc/kernel/pdc_cons.c
> > +++ b/arch/parisc/kernel/pdc_cons.c
> > @@ -272,15 +267,17 @@ void pdc_console_restart(bool hpmc)
> >   	if (pdc_console_initialized)
> >   		return;
> >
> > -	if (!hpmc && console_drivers)
> > +	if (!hpmc && !hlist_empty(&console_list))
> >   		return;
> >
> >   	/* If we've already seen the output, don't bother to print it again */
> > -	if (console_drivers != NULL)
> > +	if (!hlist_empty(&console_list))
> >   		pdc_cons.flags &= ~CON_PRINTBUFFER;
> >
> > -	while ((console = console_drivers) != NULL)
> > -		unregister_console(console_drivers);
> > +	while (!hlist_empty(&console_list)) {
> > +		unregister_console(READ_ONCE(hlist_entry(console_list.first,
> > +							 struct console, node)));
>
> The READ_ONCE() is in a wrong place. This is why it did not compile.
> It should be:
>
> 		unregister_console(hlist_entry(READ_ONCE(console_list.first),
> 						struct console,
> 						node));
>
> I know that it is all hope for good. But there is also a race between
> the hlist_empty() and hlist_entry().

I wonder if pdc_console() is still needed as it is today.
When this was written, early_console and such didn't worked for parisc
as it should. That's proably why we have this register/unregister in here.

Would it make sense, and would we gain something for this printk-series,
if I'd try to convert pdc_console to a standard earlycon or earlyprintk device?

Helge