On Thu, Oct 29, 2020 at 10:15:34AM +0100, Peter Zijlstra wrote:
> On Wed, Oct 28, 2020 at 01:15:54PM -0700, Paul E. McKenney wrote:
> > On Wed, Oct 28, 2020 at 09:02:43PM +0100, Peter Zijlstra wrote:
> > > -#ifdef CONFIG_IRQ_WORK
> > > + raw_spin_lock_rcu_node(rnp);
> >
> > The caller of rcu_implicit_dynticks_qs() already holds this lock.
> > Please see the force_qs_rnp() function and its second call site,
> > to which rcu_implicit_dynticks_qs() is passed as an argument.
>
> Like this then.
This does look plausible! But I am sure that rcutorture will also
have an opinion. ;-)
Thanx, Paul
> ---
> Subject: rcu/tree: Use irq_work_queue_remote()
> From: Peter Zijlstra <pet...@infradead.org>
> Date: Wed Oct 28 11:53:40 CET 2020
>
> The effect of an self-IPI here would be setting rcu_iw_gp_seq to the
> value we just set it to (pointless) and clearing rcu_iw_pending, which
> we just set, so don't set it.
>
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> ---
> kernel/rcu/tree.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1204,6 +1204,8 @@ static int rcu_implicit_dynticks_qs(stru
> bool *ruqp;
> struct rcu_node *rnp = rdp->mynode;
>
> + raw_lockdep_assert_held_rcu_node(rnp);
> +
> /*
> * If the CPU passed through or entered a dynticks idle phase with
> * no active irq/NMI handlers, then we can safely pretend that the CPU
> @@ -1308,14 +1310,14 @@ static int rcu_implicit_dynticks_qs(stru
> resched_cpu(rdp->cpu);
> WRITE_ONCE(rdp->last_fqs_resched, jiffies);
> }
> -#ifdef CONFIG_IRQ_WORK
> if (!rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
> (rnp->ffmask & rdp->grpmask)) {
> - rdp->rcu_iw_pending = true;
> rdp->rcu_iw_gp_seq = rnp->gp_seq;
> - irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
> + if (likely(rdp->cpu != smp_processor_id())) {
> + rdp->rcu_iw_pending = true;
> + irq_work_queue_remote(rdp->cpu, &rdp->rcu_iw);
> + }
> }
> -#endif
> }
>
> return 0;
