>
> Thanks for replying to reply Paul :)
>
> > And try testing with CONFIG_RCU_STRICT_GRACE_PERIOD=y and CONFIG_PREEMPT=n.
> > Though there might be better Kconfig options to use. Those two come
> > immediately to mind.
>
> I've tested with this option via rcu torture.
> and it doesn't report any problems.
> and after commit 6d60ea03ac2d3 ("rcu: Report QS for outermost
> PREEMPT=n rcu_read_unlock() for strict GPs")
> it always makes cpu_no_qs.b.norm false whenever it calls
> rcu_report_qs_rdp in rcu_read_unlock.
>
> > But one critical piece is that softirq handlers, including the RCU_SOFTIRQ
> > handler rcu_core_si(), can be invoked upon return from interrupts.
>
> I think in that case, no problem because if it reports qs already,
> rcu_check_quiescent_state wouldn't call rcu_report_qs_rdp again.
> And if RCU_SOFTIRQ is called as soon as RCU interrupt is finished,
> it seems the fastest one to notify qs to related tree.
>
> > Another critical piece is that if a CPU is idle during any part of a
> > grace period, the grace-period kthread can report a quiescent state on
> > its behalf.
>
> I think
> 1) If timer interrupt is still programed,
> - when rcu_sched_clock_irq first reports qs, no problem
> - If qs is reported via grace period thread first,
> note_gp_chagned in rcu interrupt
> will recognize this situation by setting core_needs_qs as false,
> it doesn't call rcu_report_qs_rdp thou cpu_no_qs.b.norm is true.
>
> 2) If the timer interrupt isn't programmed,
> - rcu_gp_kthreaad reports its qs, no problem.
>
> So, I think there's no problem removing
> "rdp->cpu_no_qs.b.norm" check in rcu_report_qs_rdp.
> or wrap this condition check as WARN_ON_ONCE.
>
> > Does that help?
> Many thanks always :)
>
Hi Levi
For built with CONFIG_RCU_STRICT_GRACE_PERIOD=y and CONFIG_PREEMPT=n kernels
Consider the following scenario:
__rcu_read_unlock()
-> rcu_read_unlock_strict()
->rdp = this_cpu_ptr(&rcu_data);
->rdp->cpu_no_qs.b.norm = false;
by interrupt and return invoke rcu_core():
->rcu_check_quiescent_state()
->rdp = raw_cpu_ptr(&rcu_data);
-> rcu_check_quiescent_state(rdp);
->note_gp_changes(rdp);
-> __note_gp_changes(rnp, rdp)
start new gp
->rdp->cpu_no_qs.b.norm = true;
->rcu_report_qs_rdp(rdp);
->if (rdp->cpu_no_qs.b.norm || ...)
Thanks
Zqiang
>
> --------
> SIncerely,
> Levi.
