Re: [PATCH] tracing: Add trace_trigger kernel command line option

[Steven Rostedt]

On Thu, 20 Oct 2022 12:33:57 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index c03fd7037add..79ac31a6a87b 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2748,9 +2748,12 @@ void trace_buffered_event_disable(void)
>  			       disable_trace_buffered_event, NULL, 1);
>  	preempt_enable();
>  
> +	if (!irqs_disabled())
> +		printk("IRQS DISABLED!! before %s:%d\n", __func__, __LINE__);
>  	/* Wait for all current users to finish */
> -	if (!early_boot_irqs_disabled)
> -		synchronize_rcu();
> +	synchronize_rcu();
> +	if (!irqs_disabled())
> +		printk("IRQS DISABLED!! after %s:%d\n", __func__, __LINE__);
>  
>  	for_each_tracing_cpu(cpu) {
>  		free_page((unsigned long)per_cpu(trace_buffered_event, cpu));


Continuing the above printk()s I found the culprit.

synchronize_rcu() {
    rcu_poll_gp_seq_start_unlocked() {
	struct rcu_node *rnp = rcu_get_root();

	if (rcu_init_invoked()) {
		lockdep_assert_irqs_enabled();
		raw_spin_lock_irq_rcu_node(rnp);
	}
	rcu_poll_gp_seq_start(snap);
	if (rcu_init_invoked())
		raw_spin_unlock_irq_rcu_node(rnp);  <<-- Interrupts enabled here
   }



-- Steve