On Mon, Aug 10, 2020 at 11:06:47AM -0700, Paul E. McKenney wrote:
> On Fri, Aug 07, 2020 at 01:07:19PM -0400, Joel Fernandes (Google) wrote:
> > At least since v4.19, the FQS loop no longer reports quiescent states
> > for offline CPUs unless it is an emergency.
> >
> > This commit therefore fixes the comment in rcu_gp_init() to match the
> > current code.
> >
> > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > ---
> > kernel/rcu/tree.c | 8 +++++---
> > 1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index a49fa3b60faa..2fb66cdbfa25 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -1701,9 +1701,11 @@ static bool rcu_gp_init(void)
> >
> > /*
> > * Apply per-leaf buffered online and offline operations to the
> > - * rcu_node tree. Note that this new grace period need not wait
> > - * for subsequent online CPUs, and that quiescent-state forcing
> > - * will handle subsequent offline CPUs.
> > + * rcu_node tree. Note that this new grace period need not wait for
> > + * subsequent online CPUs, and that RCU hooks in the CPU offlining
> > + * path, when combined with checks in this function, will handle CPUs
> > + * that are currently going offline or that go offline later. Refer to
> > + * RCU's Requirements documentation about hotplug requirements as well.
> > */
> > rcu_state.gp_state = RCU_GP_ONOFF;
> > rcu_for_each_leaf_node(rnp) {
>
> Very good! I pulled this in with light edits as shown below.
> Please let me know if I messed something up.
Yes, looks good, thanks!
- Joel
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit a6117399840b963f90cc5322ef9ea7c52de639b2
> Author: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> Date: Fri Aug 7 13:07:19 2020 -0400
>
> rcu/tree: Clarify comments about FQS loop reporting quiescent states
>
> Since at least v4.19, the FQS loop no longer reports quiescent states
> for offline CPUs except in emergency situations.
>
> This commit therefore fixes the comment in rcu_gp_init() to match the
> current code.
>
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index bcc6160..59e1943 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1730,10 +1730,13 @@ static bool rcu_gp_init(void)
> raw_spin_unlock_irq_rcu_node(rnp);
>
> /*
> - * Apply per-leaf buffered online and offline operations to the
> - * rcu_node tree. Note that this new grace period need not wait
> - * for subsequent online CPUs, and that quiescent-state forcing
> - * will handle subsequent offline CPUs.
> + * Apply per-leaf buffered online and offline operations to
> + * the rcu_node tree. Note that this new grace period need not
> + * wait for subsequent online CPUs, and that RCU hooks in the CPU
> + * offlining path, when combined with checks in this function,
> + * will handle CPUs that are currently going offline or that will
> + * go offline later. Please also refer to "Hotplug CPU" section
> + * of RCU's Requirements documentation.
> */
> rcu_state.gp_state = RCU_GP_ONOFF;
> rcu_for_each_leaf_node(rnp) {
