Re: [PATCH] rcu: Break rcu_node_0 --> &rq->__lock order

Peter Zijlstra
2023-11-01T14:38:56Z

On Wed, Nov 01, 2023 at 07:21:09PM +0800, Z qiang wrote:

> > static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
> > {
> > unsigned long jtsq;
> > + int ret = 0;
> > struct rcu_node *rnp = rdp->mynode;
> >
> > /*
> > @@ -847,8 +852,8 @@ static int rcu_implicit_dynticks_qs(stru
> > (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
> > rcu_state.cbovld)) {
> > WRITE_ONCE(rdp->rcu_urgent_qs, true);
> > - resched_cpu(rdp->cpu);
> > WRITE_ONCE(rdp->last_fqs_resched, jiffies);
> > + ret = -1;
> > }
> >
>
>
> Maybe some modifications are missing here:
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index aa4c808978b8..77e7a0dc722a 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -867,8 +867,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
> if (time_after(jiffies, rcu_state.jiffies_resched)) {
> if (time_after(jiffies,
> READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
> - resched_cpu(rdp->cpu);
> WRITE_ONCE(rdp->last_fqs_resched, jiffies);
> + ret = -1;
> }
> if (IS_ENABLED(CONFIG_IRQ_WORK) &&
> !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
>
>

Bah, you're quite right, I missed that there were two sites calling
resched_cpu().

Paul, do you want a fixed up version or will you fold in the fix?