linux-kernel - [PATCH -rcu dev 3/3] RFC: rcu/tree: Read dynticks_nmi

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Message-Id: <20190816025311.241257-3-joel@joelfernandes.org>
Date:   Thu, 15 Aug 2019 22:53:11 -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 -rcu dev 3/3] RFC: rcu/tree: Read dynticks_nmi_nesting in advance

I really cannot explain this patch, but without it, the "else if" block
just doesn't execute thus causing the tick's dep mask to not be set and
causes the tick to be turned off.

I tried various _ONCE() macros but the only thing that works is this
patch.

Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 kernel/rcu/tree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 856d3c9f1955..ac6bcf7614d7 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -802,6 +802,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
 {
 	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 	long incby = 2;
+	int dnn = rdp->dynticks_nmi_nesting;
 
 	/* Complain about underflow. */
 	WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0);
@@ -826,7 +827,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
 
 		incby = 1;
 	} else if (tick_nohz_full_cpu(rdp->cpu) &&
-		   !rdp->dynticks_nmi_nesting &&
+		   !dnn &&
 		   rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
 		rdp->rcu_forced_tick = true;
 		tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
-- 
2.23.0.rc1.153.gdeed80330f-goog