linux-kernel - Re: [PATCH printk v2 2/2] printk: Avoid scheduling irq

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Message-ID: <jm64hv26zmnlyl6lu2zoodkaz5mxcykwo5kdbvv34kyyvc6ov7@vdtslu4slrux>
Date: Thu, 13 Nov 2025 14:15:09 -0500
From: Derek Barbosa <debarbos@...hat.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Petr Mladek <pmladek@...e.com>, 
	Sergey Senozhatsky <senozhatsky@...omium.org>, Steven Rostedt <rostedt@...dmis.org>, 
	Sherry Sun <sherry.sun@....com>, Jacky Bai <ping.bai@....com>, Jon Hunter <jonathanh@...dia.com>, 
	Thierry Reding <thierry.reding@...il.com>, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH printk v2 2/2] printk: Avoid scheduling irq_work on
 suspend

Hi John,

On Thu, Nov 13, 2025 at 06:12:57PM +0106, John Ogness wrote:
> 
> I assume the problem you are seeing is with the PREEMPT_RT patches
> applied (i.e. with the 8250-NBCON included). If that is the case, note
> that recent versions of the 8250 driver introduce its own irq_work that
> is also problematic. I am currently reworking the 8250-NBCON series so
> that it does not introduce irq_work.
> 

IIRC the aforementioned scenario was just recently tested with an rc5 kernel
from Torvalds' tree. Sorry for any confusion

> Since you probably are not doing anything related to modem control,
> maybe you could test with the following hack (assuming you are using a
> v6.14 or later PREEMPT_RT patched kernel).

I'll give this a shot as a follow up, thanks for the suggestion

> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 96d32db9f8872..2ad0f91ad467a 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -3459,7 +3459,7 @@ void serial8250_console_write(struct uart_8250_port *up,
>  		 * may be a context that does not permit waking up tasks.
>  		 */
>  		if (is_atomic)
> -			irq_work_queue(&up->modem_status_work);
> +			;//irq_work_queue(&up->modem_status_work);
>  		else
>  			serial8250_modem_status(up);
>  	}
> 
> > [0] https://github.com/Linutronix/linux/commit/ae173249d9028ef159fba040bdab260d80dda43f
> 
> John
> 

-- 
Derek <debarbos@...hat.com>