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

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Message-ID: <aRdC3Dd-dfoWopS1@pathway.suse.cz>
Date: Fri, 14 Nov 2025 15:55:24 +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>,
	Sherry Sun <sherry.sun@....com>, Jacky Bai <ping.bai@....com>,
	Jon Hunter <jonathanh@...dia.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Derek Barbosa <debarbos@...hat.com>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH printk v2 2/2] printk: Avoid scheduling irq_work on
 suspend

On Thu 2025-11-13 17:09:48, John Ogness wrote:
> Allowing irq_work to be scheduled while trying to suspend has shown
> to cause problems as some architectures interpret the pending
> interrupts as a reason to not suspend. This became a problem for
> printk() with the introduction of NBCON consoles. With every
> printk() call, NBCON console printing kthreads are woken by queueing
> irq_work. This means that irq_work continues to be queued due to
> printk() calls late in the suspend procedure.
> 
> Avoid this problem by preventing printk() from queueing irq_work
> once console suspending has begun. This applies to triggering NBCON
> and legacy deferred printing as well as klogd waiters.
> 
> Since triggering of NBCON threaded printing relies on irq_work, the
> pr_flush() within console_suspend_all() is used to perform the final
> flushing before suspending consoles and blocking irq_work queueing.
> NBCON consoles that are not suspended (due to the usage of the
> "no_console_suspend" boot argument) transition to atomic flushing.
> 
> Introduce a new global variable @console_irqwork_blocked to flag
> when irq_work queueing is to be avoided. The flag is used by
> printk_get_console_flush_type() to avoid allowing deferred printing
> and switch NBCON consoles to atomic flushing. It is also used by
> vprintk_emit() to avoid klogd waking.
> 
> Add WARN_ON_ONCE(console_irqwork_blocked) to the irq_work queuing
> functions to catch any code that attempts to queue printk irq_work
> during the suspending/resuming procedure.
> 
> Cc: <stable@...r.kernel.org> # 6.13.x because no drivers in 6.12.x
> Fixes: 6b93bb41f6ea ("printk: Add non-BKL (nbcon) console basic infrastructure")
> Closes: https://lore.kernel.org/lkml/DB9PR04MB8429E7DDF2D93C2695DE401D92C4A@DB9PR04MB8429.eurprd04.prod.outlook.com
> Signed-off-by: John Ogness <john.ogness@...utronix.de>

The changes look goot to me:

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

Best Regards,
Petr