On 05/06/24 10:15, John Ogness wrote:
...
> Yes, that probably is a good candidate for emergency mode.
>
> However, your report is also identifying a real issue:
> nbcon_cpu_emergency_flush() was implemented to be callable from
> non-emergency contexts (in which case it should do nothing). However, in
> order to check if it is an emergency context, migration needs to be
> disabled.
I see.
> Perhaps the below change can be made for v2 of this series?
Yes, this seems to cure it.
Thanks for the super quick reply and patch!
Best,
Juri
> diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
> index 4b9645e7ed70..eeaf8465f492 100644
> --- a/kernel/printk/nbcon.c
> +++ b/kernel/printk/nbcon.c
> @@ -1581,8 +1581,19 @@ void nbcon_cpu_emergency_exit(void)
> */
> void nbcon_cpu_emergency_flush(void)
> {
> + bool is_emergency;
> +
> + /*
> + * If the current context is not an emergency context, preemption
> + * might be enabled. To be sure, disable preemption when checking
> + * if this is an emergency context.
> + */
> + preempt_disable();
> + is_emergency = (*nbcon_get_cpu_emergency_nesting() != 0);
> + preempt_enable();
> +
> /* The explicit flush is needed only in the emergency context. */
> - if (*(nbcon_get_cpu_emergency_nesting()) == 0)
> + if (!is_emergency)
> return;
>
> nbcon_atomic_flush_pending();
>
