linux-kernel - Re: [PATCH printk v3 11/19] printk: nbcon: Rely on kthreads for normal operation

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Message-ID: <ZqtXMiv0ES5r91ua@pathway.suse.cz>
Date: Thu, 1 Aug 2024 11:36:50 +0200
From: Petr Mladek <pmladek@...e.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk v3 11/19] printk: nbcon: Rely on kthreads for
 normal operation

On Wed 2024-07-31 17:31:02, John Ogness wrote:
> On 2024-07-31, Petr Mladek <pmladek@...e.com> wrote:
> >> @@ -4102,8 +4139,10 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
> >>  			 * that they make forward progress, so only increment
> >>  			 * @diff for usable consoles.
> >>  			 */
> >> -			if (!console_is_usable(c, flags, true))
> >> +			if (!console_is_usable(c, flags, true) &&
> >> +			    !console_is_usable(c, flags, false)) {
> >
> > This looks weird. nbcon console can't make progress when
> > "write_atomic" is not implemented and the kthreads are not
> > running.
> >
> > I should be:
> >
> > 			if (!((console_is_usable(c, flags, true)) ||
> > 			      (console_is_usable(c, flags, false) && printk_kthreads_running))) {
> 
> I would prefer to have the printk_kthreads_running check within
> console_is_usable() for the !use_atomic case.

Makes sense.

> > That said. Do we really want to support nbcon consoles without
> > @write_atomic() callback?
> 
> We must. Graphic consoles will not be able to implement
> write_atomic(). Network and USB consoles probably will not be able to
> implement it either.

I see.

Best Regards,
Petr