linux-kernel - [tip: core/rcu] rcu: Clarify comments about FQS loop reporting quiescent states

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Message-ID: <160222533513.7002.3197971404035541858.tip-bot2@tip-bot2>
Date:   Fri, 09 Oct 2020 06:35:35 -0000
From:   "tip-bot2 for Joel Fernandes (Google)" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        "Paul E. McKenney" <paulmck@...nel.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: core/rcu] rcu: Clarify comments about FQS loop reporting
 quiescent states

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     f37599e6f06da47e49c3408afe66c5b6e83a90bd
Gitweb:        https://git.kernel.org/tip/f37599e6f06da47e49c3408afe66c5b6e83a90bd
Author:        Joel Fernandes (Google) <joel@...lfernandes.org>
AuthorDate:    Fri, 07 Aug 2020 13:07:19 -04:00
Committer:     Paul E. McKenney <paulmck@...nel.org>
CommitterDate: Mon, 24 Aug 2020 18:37:55 -07:00

rcu: 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@...lfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 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) {