linux-kernel - [PATCH 3/4] rcu: Move rcu_data.cpu_no_qs.b.exp reset to rcu_export_exp

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Date:   Thu, 16 Sep 2021 14:10:47 +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>, rcu@...r.kernel.org,
        urezki@...il.com, boqun.feng@...il.com,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        joel@...lfernandes.org
Subject: [PATCH 3/4] rcu: Move rcu_data.cpu_no_qs.b.exp reset to rcu_export_exp_rdp()

On non-preemptible RCU, move clearing of rcu_data.cpu_no_qs.b.exp to
the actual expedited quiescent state report function, in a similar way
to preemptible RCU dealing with rdp->exp_deferred_qs.

This prepares to remove the exp_deferred_qs field and generalize the use
of cpu_no_qs.b.exp to both preemptible and non-preemptible RCU.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/rcu/tree_exp.h    | 1 +
 kernel/rcu/tree_plugin.h | 6 ++----
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 4266610b4587..992f9475d243 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -256,6 +256,7 @@ static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
 static void rcu_report_exp_rdp(struct rcu_data *rdp)
 {
 	rdp->exp_deferred_qs = false;
+	rdp->cpu_no_qs.b.exp = false;
 	rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
 }
 
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 4c9aeabec242..b20634fde43d 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -849,10 +849,8 @@ static void rcu_qs(void)
 	trace_rcu_grace_period(TPS("rcu_sched"),
 			       __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
 	__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
-	if (!__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
-		return;
-	__this_cpu_write(rcu_data.cpu_no_qs.b.exp, false);
-	rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
+	if (__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
+		rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
 }
 
 /*
-- 
2.25.1