linux-kernel - [PATCH RFC tip/core/rcu 03/14] rcu/nocb: EXP Check use and usefulness of ->nocb_lock

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Date:   Fri,  2 Aug 2019 08:14:50 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH RFC tip/core/rcu 03/14] rcu/nocb: EXP Check use and usefulness of ->nocb_lock_contended

Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
 kernel/rcu/tree_plugin.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index bb906295538d..fcbd61738dff 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1513,6 +1513,7 @@ static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
 	if (raw_spin_trylock(&rdp->nocb_bypass_lock))
 		return;
 	atomic_inc(&rdp->nocb_lock_contended);
+	WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
 	smp_mb__after_atomic(); /* atomic_inc() before lock. */
 	raw_spin_lock(&rdp->nocb_bypass_lock);
 	smp_mb__before_atomic(); /* atomic_dec() after lock. */
@@ -1531,7 +1532,8 @@ static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
  */
 static void rcu_nocb_wait_contended(struct rcu_data *rdp)
 {
-	while (atomic_read(&rdp->nocb_lock_contended))
+	WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
+	while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)))
 		cpu_relax();
 }
 
-- 
2.17.1