linux-kernel - [PATCH 06/10] rcu: Make nocb

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Date:   Wed, 13 May 2020 18:47:10 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E . McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>
Subject: [PATCH 06/10] rcu: Make nocb_cb kthread parkable

This will be necessary to correctly implement rdp de-offloading. We
don't want rcu_do_batch() in nocb_cb kthread to race with local
rcu_do_batch().

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Paul E. McKenney <paulmck@...nel.org>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Joel Fernandes <joel@...lfernandes.org>
---
 kernel/rcu/tree_plugin.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1dd3fdd675a1..43ecc047af26 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2104,7 +2104,9 @@ static void nocb_cb_wait(struct rcu_data *rdp)
 	if (needwake_gp)
 		rcu_gp_kthread_wake();
 	swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
-				 !READ_ONCE(rdp->nocb_cb_sleep));
+				    !READ_ONCE(rdp->nocb_cb_sleep) ||
+				    kthread_should_park());
+
 	if (!smp_load_acquire(&rdp->nocb_cb_sleep)) { /* VVV */
 		/* ^^^ Ensure CB invocation follows _sleep test. */
 		return;
@@ -2125,6 +2127,8 @@ static int rcu_nocb_cb_kthread(void *arg)
 	// if there are no more ready callbacks, waits for them.
 	for (;;) {
 		nocb_cb_wait(rdp);
+		if (kthread_should_park())
+			kthread_parkme();
 		cond_resched_tasks_rcu_qs();
 	}
 	return 0;
-- 
2.25.0