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

[Shrikanth Hegde <sshegde@linux.ibm.com>]

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.

> Regards,
> Boqun
> 
>>