[PATCH rcu 1/2] rcu/nocb: Use switch/case on NOCB timer state machine

[Paul E. McKenney]

From: Frederic Weisbecker <frede...@kernel.org>

It's more convenient to benefit from the fallthrough feature of
switch / case to handle the timer state machine. Also a new state is
about to be added that will take advantage of it.

No intended functional change.

Signed-off-by: Frederic Weisbecker <frede...@kernel.org>
Signed-off-by: Paul E. McKenney <paul...@kernel.org>
---
 kernel/rcu/tree_nocb.h | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 2605dd234a13c..0923d60c5a338 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -271,22 +271,35 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int 
waketype,
 
        raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
 
-       /*
-        * Bypass wakeup overrides previous deferments. In case of
-        * callback storms, no need to wake up too early.
-        */
-       if (waketype == RCU_NOCB_WAKE_LAZY &&
-           rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) {
-               mod_timer(&rdp_gp->nocb_timer, jiffies + 
rcu_get_jiffies_lazy_flush());
-               WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
-       } else if (waketype == RCU_NOCB_WAKE_BYPASS) {
+       switch (waketype) {
+       case RCU_NOCB_WAKE_BYPASS:
+               /*
+                * Bypass wakeup overrides previous deferments. In case of
+                * callback storms, no need to wake up too early.
+                */
                mod_timer(&rdp_gp->nocb_timer, jiffies + 2);
                WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
-       } else {
+               break;
+       case RCU_NOCB_WAKE_LAZY:
+               if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) {
+                       mod_timer(&rdp_gp->nocb_timer, jiffies + 
rcu_get_jiffies_lazy_flush());
+                       WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
+               }
+               /*
+                * If the timer is already armed, a non-lazy enqueue may have 
happened
+                * in-between. Don't delay it and fall-through.
+                */
+               break;
+       case RCU_NOCB_WAKE:
+               fallthrough;
+       case RCU_NOCB_WAKE_FORCE:
                if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE)
                        mod_timer(&rdp_gp->nocb_timer, jiffies + 1);
                if (rdp_gp->nocb_defer_wakeup < waketype)
                        WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
+               break;
+       default:
+               WARN_ON_ONCE(1);
        }
 
        raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
-- 
2.40.1