On Wed, 28 Feb 2024 14:19:11 -0800
"Paul E. McKenney" [off-list ref] wrote:

quoted

quoted

Well, to your initial point, cond_resched() does eventually invoke
preempt_schedule_common(), so you are quite correct that as far as
Tasks RCU is concerned, cond_resched() is not a quiescent state.  

 Thanks for confirming. :-)  

However, given that the current Tasks RCU use cases wait for trampolines
to be evacuated, Tasks RCU could make the choice that cond_resched()
be a quiescent state, for example, by adjusting rcu_all_qs() and
.rcu_urgent_qs accordingly.

But this seems less pressing given the chance that cond_resched() might
go away in favor of lazy preemption.

Although cond_resched() is technically a "preemption point" and not truly a
voluntary schedule, I would be happy to state that it's not allowed to be
called from trampolines, or their callbacks. Now the question is, does BPF
programs ever call cond_resched()? I don't think they do.

[ Added Alexei ]

-- Steve