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Date:   Thu, 20 Oct 2022 13:05:28 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Tom Zanussi <zanussi@kernel.org>
Subject: Re: [PATCH] tracing: Add trace_trigger kernel command line option
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On Thu, 20 Oct 2022 12:33:57 -0400
Steven Rostedt <rostedt@goodmis.org> 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