On 2025-11-11, Petr Mladek pmladek@suse.com wrote:
Introduce a new global variable @console_offload_blocked to flag
s/console_offload_blocked/console_irqwork_blocked/
Ack.
when irq_work queueing is to be avoided. The flag is used by printk_get_console_flush_type() to avoid allowing deferred printing and switch NBCON consoles to atomic flushing. It is also used by vprintk_emit() to avoid klogd waking.
--- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -230,6 +230,8 @@ struct console_flush_type { bool legacy_offload; }; +extern bool console_irqwork_blocked;
/*
- Identify which console flushing methods should be used in the context of
- the caller.
@@ -241,7 +243,7 @@ static inline void printk_get_console_flush_type(struct console_flush_type *ft) switch (nbcon_get_default_prio()) { case NBCON_PRIO_NORMAL: if (have_nbcon_console && !have_boot_console) {
if (printk_kthreads_running)
if (printk_kthreads_running && !console_irqwork_blocked) ft->nbcon_offload = true; else ft->nbcon_atomic = true;@@ -251,7 +253,7 @@ static inline void printk_get_console_flush_type(struct console_flush_type *ft) if (have_legacy_console || have_boot_console) { if (!is_printk_legacy_deferred()) ft->legacy_direct = true;
else
else if (!console_irqwork_blocked) ft->legacy_offload = true;This is one possibility.
Another possibility would be to block the irq work directly in defer_console_output() and wake_up_klogd(). It would handle all situations, including printk_trigger_flush() or defer_console_output().
Or is there any reason, why these two call paths are not handled?
My intention was to focus only on irq_work triggered directly by printk() calls as well as transitioning NBCON from threaded to direct.
I do not have strong opinion. This patch makes it more explicit when defer_console_output() or wake_up_klogd() is called.
If we move the check into defer_console_output() or wake_up_klogd(), it would hide the behavior. But it will make the API more safe to use. And wake_up_klogd() is even exported via <linux/printk.h>.
Earlier test versions of this patch did exactly as you are suggesting here. But I felt like "properly avoiding" deferred/offloaded printing via printk_get_console_flush_type() (rather than just hacking irq_work_queue() callers to abort) was a cleaner solution. Especially since printk_get_console_flush_type() modifications were needed anyway in order to transition NBCON from threaded to direct.
@@ -264,7 +266,7 @@ static inline void printk_get_console_flush_type(struct console_flush_type *ft) if (have_legacy_console || have_boot_console) { if (!is_printk_legacy_deferred()) ft->legacy_direct = true;
else
else if (!console_irqwork_blocked) ft->legacy_offload = true;This change won't be needed if we move the check into defer_console_output() and wake_up_klogd().
} break;diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 5aee9ffb16b9a..94fc4a8662d4b 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2426,7 +2429,7 @@ asmlinkage int vprintk_emit(int facility, int level, if (ft.legacy_offload) defer_console_output();
- else
- else if (!console_irqwork_blocked) wake_up_klogd();
Same here.
return printed_len;
I would prefer to keep all the printk_get_console_flush_type() changes since it returns proper available flush type information. If you would like to _additionally_ short-circuit __wake_up_klogd() and nbcon_kthreads_wake() in order to avoid all possible irq_work queueing, I would be OK with that.
John