linux-kernel - [PATCH v4 2/5] rcu/tree: Clarify comments about FQS loop reporting quiescent states

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Date:   Fri,  7 Aug 2020 13:07:19 -0400
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Jonathan Corbet <corbet@....net>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-doc@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        neeraju@...eaurora.org, "Paul E. McKenney" <paulmck@...nel.org>,
        peterz@...radead.org, Randy Dunlap <rdunlap@...radead.org>,
        rcu@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        tglx@...utronix.de, vineethrp@...il.com
Subject: [PATCH v4 2/5] rcu/tree: Clarify comments about FQS loop reporting quiescent states

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@...lfernandes.org>
---
 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) {
-- 
2.28.0.236.gb10cc79966-goog