Re: [PATCH v2] kcsan: Don't enter an nbcon emergency section for verbose reports

[Breno Leitao <leitao@debian.org>]

On Wed, Nov 04, 2026 at 01:52:41PM +0106, John Ogness wrote:
> On 2026-11-04, Breno Leitao <leitao@debian.org> wrote:
> > Since commit 59cd94ef8009 ("lockdep: Mark emergency sections in lockdep
> > splats"), print_irqtrace_events() runs inside an nbcon emergency
> > section. It is not only used by lockdep splats, though: verbose KCSAN
> > reports call it too, and a data race report is not an emergency. Yet in
> > an emergency section, every printk() flushes all pending records to the
> > nbcon consoles from the calling context, instead of leaving them to the
> > printk threads.
> 
> Wouldn't the below diff be the proper fix?
> 
> John
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index c3dc84a7cef26..71f1b4b8f06d5 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -4245,8 +4245,6 @@ void print_irqtrace_events(struct task_struct *curr)
>  {
>  	const struct irqtrace_events *trace = &curr->irqtrace;
>  
> -	nbcon_cpu_emergency_enter();
> -
>  	printk("irq event stamp: %u\n", trace->irq_events);
>  	printk("hardirqs last  enabled at (%u): [<%px>] %pS\n",
>  		trace->hardirq_enable_event, (void *)trace->hardirq_enable_ip,
> @@ -4260,8 +4258,6 @@ void print_irqtrace_events(struct task_struct *curr)
>  	printk("softirqs last disabled at (%u): [<%px>] %pS\n",
>  		trace->softirq_disable_event, (void *)trace->softirq_disable_ip,
>  		(void *)trace->softirq_disable_ip);
> -
> -	nbcon_cpu_emergency_exit();
>  }
>  
>  static int HARDIRQ_verbose(struct lock_class *class)
> @@ -5797,8 +5793,11 @@ static noinstr void check_flags(unsigned long flags)
>  	}
>  #endif
>  
> -	if (!debug_locks)
> +	if (!debug_locks) {
> +		nbcon_cpu_emergency_enter();
>  		print_irqtrace_events(current);
> +		nbcon_cpu_emergency_exit();
> +	}
>  
>  	instrumentation_end();
>  #endif

Yes, but it was unclear to me what were the invocations of
print_irqtrace_events() that needed the emergency turned on.

how did you decided that only check_flags() needed it?

Thanks for the review,
--breno