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 :)
--------
SIncerely,
Levi.
