Re: [PATCH v2] printk_legacy_map: use LD_WAIT_CONFIG instead of LD_WAIT_SLEEP

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

On 2025-10-23, Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
>> @@ -3016,7 +3017,7 @@ bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
>>  static inline void printk_legacy_allow_spinlock_enter(void) { }
>>  static inline void printk_legacy_allow_spinlock_exit(void) { }
>>  #else
>> -static DEFINE_WAIT_OVERRIDE_MAP(printk_legacy_map, LD_WAIT_SLEEP);
>> +static DEFINE_WAIT_OVERRIDE_MAP(printk_legacy_map, LD_WAIT_CONFIG);
>
> We could use this lock_map_acquire_try() directly but okay having it in
> one spot with a comment might have its benefit. But _why_ is here a
> CONFIG_PREEMPT_RT? This is supposed to work in both cases. Should a
> legacy driver be invoked on RT then the comment is not accurate, lockdep
> won't yell but we still have CONFIG_DEBUG_ATOMIC_SLEEP making its own
> judgement.

With PREEMPT_RT, legacy console printing is forced into its own
dedicated kthread. At runtime this is checked via
force_legacy_kthread(). So with PREEMPT_RT there is no need for special
lockdep trickery. Once we can get all the consoles switched over to
nbcon, !PREEMPT_RT will also not need this lockdep trickery.

John