[PATCH tip/core/rcu 20/24] rcu: Clarify comments about FQS loop reporting quiescent states

[paulmck]

From: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>

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>
---
 kernel/rcu/tree.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 52108dd..2c7afe4 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1706,10 +1706,13 @@ 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) {
-- 
2.9.5