linux-kernel - Re: [PATCH 1/7] printk: Make console_{suspend,resume} handle CON

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Message-ID: <49eed036f3c230d066ff44620c222fe5a2c3da1a.camel@suse.com>
Date: Mon, 23 Jun 2025 15:45:37 -0300
From: Marcos Paulo de Souza <mpdesouza@...e.com>
To: Petr Mladek <pmladek@...e.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, John Ogness	
 <john.ogness@...utronix.de>, Sergey Senozhatsky <senozhatsky@...omium.org>,
  Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby
 <jirislaby@...nel.org>, Jason Wessel	 <jason.wessel@...driver.com>, Daniel
 Thompson <danielt@...nel.org>, Douglas Anderson <dianders@...omium.org>,
 Richard Weinberger <richard@....at>, Anton Ivanov	
 <anton.ivanov@...bridgegreys.com>, Johannes Berg
 <johannes@...solutions.net>, 	linux-kernel@...r.kernel.org,
 linux-serial@...r.kernel.org, 	kgdb-bugreport@...ts.sourceforge.net,
 linux-um@...ts.infradead.org
Subject: Re: [PATCH 1/7] printk: Make console_{suspend,resume} handle
 CON_SUSPENDED

On Thu, 2025-06-12 at 13:46 +0200, Petr Mladek wrote:
> On Fri 2025-06-06 23:53:43, Marcos Paulo de Souza wrote:
> > Since commit 9e70a5e109a4 ("printk: Add per-console suspended
> > state") the
> > CON_SUSPENDED flag was introced, and this flag was being checked on
> > console_is_usable function, which returns false if the console is
> > suspended.
> > 
> > No functional changes.
> 
> I double checked potential functional changes. In particular, I
> checked where the CON_ENABLED and CON_SUSPENDED flags were used.
> 
> Both flags seems to have the same effect in most situations,
> for example, in console_is_usable() or console_unblank().
> 
> But there seems to be two exceptions: kdb_msg_write() and
> show_cons_active(). These two functions check only
> the CON_ENABLED flag. And they think that the console is
> usable when the flag is set.
> 
> The change in this patch would change the behavior of the two
> functions during suspend. It is later fixed by the 3rd and 4th
> patch. But it might cause regressions during bisections.
> 
> It is probably not a big deal because the system is not much
> usable during the suspend anyway. But still, I would feel more
> comfortable if we prevented the "temporary" regression.
> 
> I see two possibilities:
> 
>    1. Merge the 3rd and 4th patch into this one. It would change
>       the semantic in a single patch.

I liked the suggestion, I'll do it in the next revision. Thanks for
looking into it!

> 
>    2. First update kdb_msg_write() and show_cons_active()
>       to check both CON_ENABLE and CON_SUSPENDED flags.
> 
> The 1st solution probably makes more sense because we are going
> to remove the CON_ENABLE flag in the end. And even the merged
> patch is small enough.
> 
> Best Regards,
> Petr