linux-kernel - Re: replay log: Re: [PATCH printk v4 38/39] printk: relieve console

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Message-ID: <Y3PBNJRvE6tU8ct+@alley>
Date:   Tue, 15 Nov 2022 17:41:24 +0100
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: replay log: Re: [PATCH printk v4 38/39] printk: relieve
 console_lock of list synchronization duties

On Tue 2022-11-15 16:34:10, Petr Mladek wrote:
> On Mon 2022-11-14 17:35:31, John Ogness wrote:
> > The console_list_lock provides synchronization for console list and
> > console->flags updates. All call sites that were using the console_lock
> > for this synchronization have either switched to use the
> > console_list_lock or the SRCU list iterator.
> > 
> > Remove console_lock usage for console list updates and console->flags
> > updates.
> > 
> > Signed-off-by: John Ogness <john.ogness@...utronix.de>
> 
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -3334,6 +3330,11 @@ void register_console(struct console *newcon)
> >  		 * boot console that is the furthest behind.
> >  		 */
> >  		if (bootcon_registered && !keep_bootcon) {
> > +			/*
> > +			 * Hold the console_lock to guarantee safe access to
> > +			 * console->seq.
> > +			 */
> > +			console_lock();
> >  			for_each_console(con) {
> >  				if ((con->flags & CON_BOOT) &&
> >  				    (con->flags & CON_ENABLED) &&
> > @@ -3341,6 +3342,7 @@ void register_console(struct console *newcon)
> >  					newcon->seq = con->seq;
> >  				}
> >  			}
> > +			console_unlock();
> 
> Thinking more about it. This console_unlock() will actually cause
> flushing the boot consoles. A solution would be to call
> console_flush_all() here.
> 
> And we could/should solve this in a separate patch. This code was not locked
> before. It is a corner case. It could be solved later.
> 
> >  		}
> >  	}
> >  

The rest of the patch looks fine. I checked hopefully console_list walks
and console flags manipulations and everything looks good.

So, without the above two hunks:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr