linux-kernel - Re: [PATCH] printk/nbcon: Restore IRQ in atomic flush after each emitted record

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Message-ID: <aTFgdQNeKb0k4SQS@pathway.suse.cz>
Date: Thu, 4 Dec 2025 11:20:37 +0100
From: Petr Mladek <pmladek@...e.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Leo Yan <leo.yan@....com>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Breno Leitao <leitao@...ian.org>, linux@...linux.org.uk,
	paulmck@...nel.org, usamaarif642@...il.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel-team@...a.com, rmikey@...a.com
Subject: Re: [PATCH] printk/nbcon: Restore IRQ in atomic flush after each
 emitted record

On Wed 2025-12-03 13:33:38, John Ogness wrote:
> On 2025-12-02, Leo Yan <leo.yan@....com> wrote:
> >> I am not really happy about all the local_irq_restore() usage. Using
> >> guard syntax would be nice here, but AFAICT there is no guard for
> >> local_irq_save()/_restore().
> >
> > Sorry for suddenly jumping in.  Wouldn't guard(irqsave)() be helpful
> > here?
> 
> Thanks, I was not aware of the irqsave variant. We would want the scoped
> version. So something like this?
> 
> $ git diff -w
> diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
> index 3fa403f9831f..55beb64c4f4a 100644
> --- a/kernel/printk/nbcon.c
> +++ b/kernel/printk/nbcon.c
> @@ -1557,6 +1557,14 @@ static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq)
>  	ctxt->allow_unsafe_takeover	= nbcon_allow_unsafe_takeover();
>  
>  	while (nbcon_seq_read(con) < stop_seq) {
> +		/*
> +		 * Atomic flushing does not use console driver synchronization
> +		 * (i.e. it does not hold the port lock for uart consoles).
> +		 * Therefore IRQs must be disabled to avoid being interrupted
> +		 * and then calling into a driver that will deadlock trying
> +		 * to acquire console ownership.
> +		 */
> +		scoped_guard(irqsave) {
>  			if (!nbcon_context_try_acquire(ctxt, false))
>  				return -EPERM;
>  
> @@ -1569,6 +1577,7 @@ static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq)
>  				return -EAGAIN;
>  
>  			nbcon_context_release(ctxt);
> +		}
>  
>  		if (!ctxt->backlog) {
>  			/* Are there reserved but not yet finalized records? */
> 

Great. Thanks for hint. I am going to send v2 with this change.

Best Regards,
Petr