linux-kernel - Re: [PATCH v2] printk/console: Enable console kthreads only when there is no boot console left

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Date:   Wed, 22 Jun 2022 11:55:36 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        John Ogness <john.ogness@...utronix.de>,
        Marek Behún <kabel@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jan Kara <jack@...e.cz>, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] printk/console: Enable console kthreads only when
 there is no boot console left

On (22/06/21 13:19), Petr Mladek wrote:
> > > -static int __init printk_activate_kthreads(void)
> > > -{
> > > -	struct console *con;
> > >  
> > > -	console_lock();
> > > -	printk_kthreads_available = true;
> > > -	for_each_console(con)
> > > -		printk_start_kthread(con);
> > > -	console_unlock();
> > > +	/*
> > > +	 * Boot consoles may be accessing the same hardware as normal
> > > +	 * consoles and thus must not be called in parallel. Therefore
> > > +	 * only activate threaded console printing if it is known that
> > > +	 * there are no boot consoles registered.
> > > +	 */
> > > +	if (no_bootcon)
> > > +		printk_activate_kthreads();
> > 
> > A quick question. Here we still can have bootcon which can unregistered
> > later, right? Do you think it'll make sense to check if printing kthreads
> > can be safely started and start them if so (if no CON_BOOT found and kthreads
> > are not already created) at the end of unregister_console()?
> 
> Yeah, that's my plan how to optimize it in the future. I just
> wanted to do something simple and be on the safe side for 5.19.

Sounds good.