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

[Shrikanth Hegde]

On 5/20/26 10:22 PM, Steven Rostedt wrote:
> On Wed, 20 May 2026 12:03:37 +0530
> Shrikanth Hegde <sshegde@xxxxxxxxxxxxx> 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?
> > >