On Thu, May 28, 2026 at 12:43:22PM +0200, Peter Zijlstra wrote:
> 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();
>
I was trying to not re-invent the wheel for "checking whether we can
preempt" (because the definition of preempt condition might be changed
in the future?), but yes I think directly using new_count should be fine
here. Although I think I need to check tif_need_resched() for other
architectures?
Regards,
Boqun
> > +#endif
> > + }
> > +}
> > +
> > +#endif /* !__LINUX_INTERRUPT_RC_H */
