Re: [PATCH] nbcon/reboot: Flush nbcon consoles synchronously on reboot

[Bradley Morgan]

On 8 October 2026 16:08:52 BST, Petr Mladek <pmladek@xxxxxxxx> wrote:
>NBCON consoles emit messages in a dedicated kthreads when the system
>is working properly. printk() tries to flush them synchronously in
>explicitly marked emergency context and in panic().
>
>Another situation where printk() could not rely on kthreads are the
>various
>reboot and halt code paths. They can be detected by the `system_state`
>variable.
>
>Let's default to NBCON_PRIO_EMERGENCY for the post-running states.
>printk() will automatically try flushing the consoles synchronously.
>Also do not rely on printk() and explicitly flush the consoles
>after these states are set.
>
>Note that suspend code paths have already been handled, see
>console_suspend_all() and console_suspend().
>
>Reported-by: kernel test robot <lkp@xxxxxxxxx>
>Closes: https://lore.kernel.org/all/202608061008.48a1e76e-lkp@xxxxxxxxx/
>Suggested-by: John Ogness <john.ogness@xxxxxxxxxxxxx>

Hi, this looks good to me reboot.c ended! :)

Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>

>Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
>---
>Hi,
>
>ah, this somehow fallen through cracks.
>I am sending it as a proper patch finally.
>
>I am sorry I have been somehow too busy before
>the Plumbers conference.

That's ok :) I'm too unlucky as to not go to any conferences :c

>
>Best Regards,
>Petr
>---
> kernel/printk/nbcon.c | 4 ++++
> kernel/reboot.c       | 4 ++++
> 2 files changed, 8 insertions(+)
>
>diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
>index fb1b37741952..d8f8ec836eea 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();
> }
>

--- Thanks!
"I'm not a very positive person" - Linus torvalds