linux-kernel - [PATCH v2 -rcu dev 2/3] rcu/tree: Fix issue where sometimes rcu_urgent

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Message-ID: <20190816025914.GB242309@google.com>
Date:   Thu, 15 Aug 2019 22:59:14 -0400
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        rcu@...r.kernel.org, "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        frederic@...nel.org
Subject: [PATCH v2 -rcu dev 2/3] rcu/tree: Fix issue where sometimes
 rcu_urgent_qs is not set on IPI

Sometimes I see rcu_urgent_qs is not set. This could be when the last
IPI was a long time ago, however, the grace period just started. Set
rcu_urgent_qs so the tick can indeed not be stopped.

Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 kernel/rcu/tree.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 322b1b57967c..856d3c9f1955 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1091,6 +1091,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	if (tick_nohz_full_cpu(rdp->cpu) &&
 		   time_after(jiffies,
 			      READ_ONCE(rdp->last_fqs_resched) + jtsq * 3)) {
+		WRITE_ONCE(*ruqp, true);
 		resched_cpu(rdp->cpu);
 		WRITE_ONCE(rdp->last_fqs_resched, jiffies);
 	}
-- 
2.23.0.rc1.153.gdeed80330f-goog