Re: [linux-next:master] [serial] d353934702: BUG:kernel_reboot-without-warning_in_test_stage

[John Ogness <john.ogness@linutronix.de>]

On 2026-09-23, Petr Mladek <pmladek@suse.com> wrote:
> The above patch handles only emergency_restart(). The similar problem
> would be even in other code paths where the system is going down.
> I think about using NBCON_EMERGENCY_PRIO automatically in all
> these states, something like:
>
> diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
> index d17704fe93ae..48446926dc50 100644
> --- a/kernel/printk/nbcon.c
> +++ b/kernel/printk/nbcon.c
> @@ -1446,6 +1446,10 @@ enum nbcon_prio nbcon_get_default_prio(void)
>  	if (panic_on_this_cpu())
>  		return NBCON_PRIO_PANIC;
>  
> +	/* Do not rely on kthreads when the system is going down. */
> +	if (system_state > SYSTEM_RUNNING)
> +		return NBCON_PRIO_EMERGENCY;
> +
>  	cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
>  	if (*cpu_emergency_nesting)
>  		return NBCON_PRIO_EMERGENCY;
> diff --git a/kernel/reboot.c b/kernel/reboot.c
> index d177d89fcc33..776784a82499 100644
> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -8,6 +8,7 @@
>  #define pr_fmt(fmt)	"reboot: " fmt
>  
>  #include <linux/atomic.h>
> +#include <linux/console.h>
>  #include <linux/ctype.h>
>  #include <linux/export.h>
>  #include <linux/kexec.h>
> @@ -94,6 +95,7 @@ void emergency_restart(void)
>  {
>  	kmsg_dump(KMSG_DUMP_EMERG);
>  	system_state = SYSTEM_RESTART;
> +	printk_trigger_flush();
>  	machine_emergency_restart();
>  }
>  EXPORT_SYMBOL_GPL(emergency_restart);
> @@ -102,6 +104,7 @@ void kernel_restart_prepare(char *cmd)
>  {
>  	blocking_notifier_call_chain(&reboot_notifier_list, SYS_RESTART, cmd);
>  	system_state = SYSTEM_RESTART;
> +	printk_trigger_flush();
>  	usermodehelper_disable();
>  	device_shutdown();
>  }
> @@ -305,6 +308,7 @@ static void kernel_shutdown_prepare(enum system_states state)
>  	blocking_notifier_call_chain(&reboot_notifier_list,
>  		(state == SYSTEM_HALT) ? SYS_HALT : SYS_POWER_OFF, NULL);
>  	system_state = state;
> +	printk_trigger_flush();
>  	usermodehelper_disable();
>  	device_shutdown();
>  }
>
> Note that it would use NBCON_EMERGENCY_PRIO even in SYSTEM_SUSPEND
> state. But I think that it does not have any real effect because
> it seems to be done after the consoles are suspended. at least
> in hibernation_platform_enter().

And we transition to atomic printing for suspend anyway if
"no_console_suspend" is specified.

I am OK with this change. My only concern is that it is best effort. If
some of these callbacks are always called from task context, using an
_additional_ pr_flush() might make sense.

John