Re: [PATCH v2] sched/rt: Have RT_PUSH_IPI be default off for non PREEMPT_RT

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

On 5/20/26 10:22 PM, Steven Rostedt wrote:
> On Wed, 20 May 2026 12:03:37 +0530
> Shrikanth Hegde <sshegde@linux.ibm.com> wrote:
> 
>> On 5/18/26 2:17 PM, Valentin Schneider wrote:
>>> On 15/05/26 10:37, Steven Rostedt wrote:
>>
>>> I got a bit confused here, please correct me if I didn't get this right:
>>>
>>> Per handle_softirqs(), we can't restart the softirq handling loop if
>>> need_resched() is true (which would be the case here, per what we'd have
>>> done it push_rt_task(@pull=true)).
>>> I thought this meant softirqs couldn't be the issue, however this is only
>>> valid within the scope of a single handle_softirqs() invocation.
>>>
>>> AIUI here we're being hammered by IRQs, thus under this sort of pattern:
>>>
>>> <IRQ>
>>>     __irq_exit_rcu()
>>>       invoke_softirq()
>>>         handle_softirqs()
>>>           // handle NET_RX_SOFTIRQ
>>>           // need_resched() is true so don't loop
>>> </IRQ>
>>>    
>>
>> Wouldn't IRQ exit call schedule if need_resched is set? via irqentry_exit_cond_resched ?
> 
> I haven't looked at the networking code, but does NAPI just continue
> looping while there are packets to process? Or is there a check if
> need_resched() is set, that it will exit out early?
> 
> Yeah, I'm still wondering why this causes a live lock.
> 
> -- Steve
> 
> 

By any chance it is running with preempt=none/voluntary?
If so it might never call schedule until it goes back to user space.

>>
>>> // Barely any progress made here towards actually executing __schedule()
>>>
>>> <IRQ>
>>>     __irq_exit_rcu()
>>>       invoke_softirq()
>>>         handle_softirqs()
>>>           // handle NET_RX_SOFTIRQ and wake up some tasks
>>>           // need_resched() is true so don't loop
>>> </IRQ>
>>>
>>> & repeat ad nauseam. Did I get this right?
>>>    
>