Re: [PATCH v2 05/12] irq & spin_lock: Add counted interrupt disabling/enabling

[Peter Zijlstra <peterz@infradead.org>]

On Tue, May 26, 2026 at 08:21:41AM -0700, Boqun Feng wrote:

> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index e2d3079d3f5f..33fc4c814a9f 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -151,6 +151,10 @@ static __always_inline unsigned char interrupt_context_level(void)
>  #define in_softirq()		(softirq_count())
>  #define in_interrupt()		(irq_count())
>  
> +#define hardirq_disable_count()	((preempt_count() & HARDIRQ_DISABLE_MASK) >> HARDIRQ_DISABLE_SHIFT)
> +#define hardirq_disable_enter()	__preempt_count_add_return(HARDIRQ_DISABLE_OFFSET)
> +#define hardirq_disable_exit()	__preempt_count_sub_return(HARDIRQ_DISABLE_OFFSET)
> +
>  /*
>   * The preempt_count offset after preempt_disable();
>   */

> diff --git a/include/linux/interrupt_rc.h b/include/linux/interrupt_rc.h
> new file mode 100644
> index 000000000000..868f32524a87
> --- /dev/null
> +++ b/include/linux/interrupt_rc.h
> @@ -0,0 +1,65 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * include/linux/interrupt_rc.h - refcounted local processor interrupt
> + * management.
> + *
> + * Since the implementation of this API currently depends on
> + * local_irq_save()/local_irq_restore(), we split this into it's own header to
> + * make it easier to include without hitting circular header dependencies.
> + */
> +
> +#ifndef __LINUX_INTERRUPT_RC_H
> +#define __LINUX_INTERRUPT_RC_H
> +
> +#include <linux/irqflags.h>
> +#include <asm/processor.h>
> +#ifdef CONFIG_SMP
> +#include <asm/smp.h>
> +#endif
> +
> +/* Per-cpu interrupt disabling state for local_interrupt_{disable,enable}() */
> +struct interrupt_disable_state {
> +	unsigned long flags;
> +};
> +
> +DECLARE_PER_CPU(struct interrupt_disable_state, local_interrupt_disable_state);
> +
> +static inline void local_interrupt_disable(void)
> +{
> +	unsigned long flags;
> +	int new_count;
> +
> +	new_count = hardirq_disable_enter();
> +
> +	/* Interrupts can happen here, but it's OK, see __irq_exit_rcu(). */
> +
> +	if ((new_count & HARDIRQ_DISABLE_MASK) == HARDIRQ_DISABLE_OFFSET) {
> +		local_irq_save(flags);
> +		raw_cpu_write(local_interrupt_disable_state.flags, flags);
> +	}
> +}
> +
> +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 CONFIG_PREEMPTION
> +		if (should_resched(0))
> +			__preempt_schedule();

I'm not sure why you bother with should_resched() at this point, can't
you simply write:

		if (!new_count)
			__preempt_schedule();

> +#endif
> +	}
> +}
> +
> +#endif /* !__LINUX_INTERRUPT_RC_H */