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

[Boqun Feng]

On Wed, Aug 05, 2026 at 12:39:36PM +0530, Shrikanth Hegde wrote:
> 
> 
> On 8/5/26 12:37 PM, Boqun Feng wrote:
> > 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.
> > 
> 
> I was suggesting to have a mechanism which allows to debug it/
> find the callers.
> 

Ok, I can reuse the DEBUG_PREEMPT kconfig and the DEBUG_LOCKS_WARN_ON()
here, but it'll be similar to the detection here, not a 256 maximum
nesting but a 256 - 10 value (and I'm not going to explain why we think
10 is a good buffer, unless you think we should have a discussion about
it ;-) )


(But still who is going to add the detection for BH count over? ;-) )

Regards,
Boqun

> > Regards,
> > Boqun
> > 
> > > 
>