On Sat, Dec 31, 2022 at 07:25:08PM +0100, Frederic Weisbecker wrote:
> On Wed, Dec 21, 2022 at 12:08:49PM -0800, Paul E. McKenney wrote:
> > diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> > index 249c2967d9e6c..7cc4856da0817 100644
> > --- a/kernel/rcu/tree_exp.h
> > +++ b/kernel/rcu/tree_exp.h
> > @@ -594,6 +594,7 @@ static void synchronize_rcu_expedited_wait(void)
> > struct rcu_data *rdp;
> > struct rcu_node *rnp;
> > struct rcu_node *rnp_root = rcu_get_root();
> > + unsigned long flags;
> >
> > trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
> > jiffies_stall = rcu_exp_jiffies_till_stall_check();
> > @@ -602,17 +603,17 @@ static void synchronize_rcu_expedited_wait(void)
> > if (synchronize_rcu_expedited_wait_once(1))
> > return;
> > rcu_for_each_leaf_node(rnp) {
> > + raw_spin_lock_irqsave_rcu_node(rnp, flags);
> > mask = READ_ONCE(rnp->expmask);
> > for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
> > rdp = per_cpu_ptr(&rcu_data, cpu);
> > if (rdp->rcu_forced_tick_exp)
> > continue;
> > rdp->rcu_forced_tick_exp = true;
> > - preempt_disable();
> > if (cpu_online(cpu))
> > tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
> > - preempt_enable();
> > }
> > + raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> > }
> > j = READ_ONCE(jiffies_till_first_fqs);
> > if (synchronize_rcu_expedited_wait_once(j + HZ))
>
> Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Thank you!
> BTW why are we forcing the tick on the whole node?
Now that you mention it, that would be more precise.
> And shouldn't we set the tick dependency from rcu_exp_handler() instead?
Because it never occurred to me to check whether this could be invoked
from an interrupt handler? ;-)
But that does sound like it might be a better approach.
Zqiang, would you be willing to look into this?
Thanx, Paul
