Re: [RFC RESEND v10 03/14] irq & spin_lock: Add counted interrupt disabling/enabling

[Steven Rostedt]

On Tue, 27 May 2025 18:21:44 -0400
Lyude Paul <lyude@xxxxxxxxxx> wrote:

> +static inline void local_interrupt_enable(void)
> +{
> +	int new_count;
> +
> +	new_count = hardirq_disable_exit();
> +
> +	if ((new_count & HARDIRQ_DISABLE_MASK) == 0) {
> +		unsigned long flags;
> +
> +		flags = raw_cpu_read(local_interrupt_disable_state.flags);
> +		local_irq_restore(flags);
> +		/*
> +		 * TODO: re-read preempt count can be avoided, but it needs
> +		 * should_resched() taking another parameter as the current
> +		 * preempt count
> +		 */
> +#ifdef PREEMPTION
> +		if (should_resched(0))
> +			__preempt_schedule();
> +#endif
> +	}
> +}

I'm confused to why the should_resched() is needed? We are handling
interrupts right? The hardirq_disable_exit() will set preempt_count to zero
before we enable interrupts. When the local_irq_restore() enables interrupts
again, if there's an interrupt pending it will trigger then. If the
interrupt sets NEED_RESCHED, when it returns from the interrupt handler, it
will see preempt_count as zero, right?

If it does, then it will call schedule before it gets back to this code.

-- Steve