Re: [PATCH 09/19] rcu/context-tracking: Remove rcu_irq_enter/exit()

[Peter Zijlstra]

On Wed, Mar 02, 2022 at 04:48:00PM +0100, Frederic Weisbecker wrote:
>  void ct_irq_enter_irqson(void)
>  {
> -	rcu_irq_enter_irqson();
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
> +	ct_irq_enter();
> +	local_irq_restore(flags);
>  }
>  
>  void ct_irq_exit_irqson(void)
>  {
> -	rcu_irq_exit_irqson();
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
> +	ct_irq_exit();
> +	local_irq_restore(flags);
>  }

I know you're just copying code around, but this is broken per
construction :/

On the irq_enter site, local_irq_save() will hit a tracepoint, which
requires RCU, which will only be made available by the ct_irq_enter().
Same in reverse for the exit case.