Re: [PATCH v4 05/17] irq & spin_lock: Add counted interrupt disabling/enabling

[Boqun Feng]

On Wed, Aug 05, 2026 at 08:36:45AM +0200, Peter Zijlstra wrote:
> On Tue, Aug 04, 2026 at 02:08:11PM -0700, Boqun Feng wrote:
> 
> > > > +	/* Interrupts can happen here, but it's OK, see __irq_exit_rcu(). */
> > > > +
> > > > +	if ((new_count & HARDIRQ_DISABLE_MASK) == HARDIRQ_DISABLE_OFFSET)
> > > > +		_local_interrupt_disable();
> > > > +}
> > > 
> > > Maximum nesting possible is 256 right? Whats is stopping here to do more than that?
> > 
> > Yes. Currently similar as softirq, we don't detect the overflow.
> > 
> > > Should there be a warn_on?
> > 
> > A simple warn_on could be problematic because warn_on() itself may take
> > an irq-disabling lock, and that may trigger another overflow on top of
> > the existing overflow. It's a bit tricky to do a proper detection. But
> > I'm open to ideas.
> 
> DEBUG_PREEMPT's preempt_count_add() does:
> 
>         DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >= PREEMPT_MASK - 10);
> 

Yeah, but this is behind a kconfig (DEBUG_PREEMPT), so not sure whether
it's what Shrikanth asked here.

Regards,
Boqun

>