linux-kernel - [PATCH] rcu: Force quiescent states only for ongoing grace period

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Message-Id: <20231101033507.21651-1-qiang.zhang1211@gmail.com>
Date:   Wed,  1 Nov 2023 11:35:07 +0800
From:   Zqiang <qiang.zhang1211@...il.com>
To:     paulmck@...nel.org, frederic@...nel.org, joel@...lfernandes.org,
        boqun.feng@...il.com
Cc:     qiang.zhang1211@...il.com, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] rcu: Force quiescent states only for ongoing grace period

Currently, when running the rcutorture testing, if the fqs_task
kthread was created, the periodic fqs operations will be performed,
regardless of whether the grace-period is ongoing. however, if there
is no ongoing grace-period, invoke the rcu_force_quiescent_state() has
no effect, because when the new grace-period starting, will clear all
flags int rcu_state.gp_flags in rcu_gp_init(). this commit therefore add
rcu_gp_in_progress() check in rcu_force_quiescent_state(), if there is
no ongoing grace-period, return directly.

Signed-off-by: Zqiang <qiang.zhang1211@...il.com>
---
 kernel/rcu/tree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index aa4c808978b8..5b4279ef66da 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2338,6 +2338,8 @@ void rcu_force_quiescent_state(void)
 	struct rcu_node *rnp;
 	struct rcu_node *rnp_old = NULL;

+	if (!rcu_gp_in_progress())
+		return;
 	/* Funnel through hierarchy to reduce memory contention. */
 	rnp = raw_cpu_read(rcu_data.mynode);
 	for (; rnp != NULL; rnp = rnp->parent) {
-- 
2.17.1