linux-kernel - Re: [PATCH printk v2 02/38] printk: Convert console

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Date:   Thu, 20 Oct 2022 09:43:04 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH printk v2 02/38] printk: Convert console_drivers list to
 hlist

On Wed, Oct 19, 2022 at 11:52:53PM +0206, John Ogness wrote:
> On 2022-10-19, Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:
> >> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> >> index e4f1e7478b52..867becc40021 100644
> >> --- a/kernel/printk/printk.c
> >> +++ b/kernel/printk/printk.c
> >> @@ -3229,32 +3244,30 @@ int unregister_console(struct console *console)
> >>  	if (res > 0)
> >>  		return 0;
> >>  
> >> -	res = -ENODEV;
> >>  	console_lock();
> >> -	if (console_drivers == console) {
> >> -		console_drivers=console->next;
> >> -		res = 0;
> >> -	} else {
> >> -		for_each_console(con) {
> >> -			if (con->next == console) {
> >> -				con->next = console->next;
> >> -				res = 0;
> >> -				break;
> >> -			}
> >> -		}
> >> +
> >> +	/* Disable it unconditionally */
> >> +	console->flags &= ~CON_ENABLED;
> >> +
> >> +	if (hlist_unhashed(&console->node)) {
> >
> > How can this ever be hit?  The console lock is held, so it shouldn't
> > have gone away already.  Or am I missing something else here?
> 
> Mainline also has this check. I expect it is for the case that some code
> tries to call unregister_console() for a console that is not
> registered.
> 
> Since register_console() does not return if it succeeded, I suppose some
> code somewhere my try to unregister without knowing that it never
> registered in the first place.

Ick, ok, that's fine for now.

What a mess, thanks for working to unwind it!

greg k-h