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From:   "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To:     linux-kernel@vger.kernel.org
Cc:     mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
        akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
        josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
        rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
        fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 04/19] rcu: Allow processing deferred QSes for exiting RCU-preempt readers
Date:   Wed, 29 Aug 2018 15:20:32 -0700
In-Reply-To: <20180829222021.GA29944@linux.vnet.ibm.com>
References: <20180829222021.GA29944@linux.vnet.ibm.com>
Message-Id: <20180829222047.319-4-paulmck@linux.vnet.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

If an RCU-preempt read-side critical section is exiting, that is,
->rcu_read_lock_nesting is negative, then it is a good time to look
at the possibility of reporting deferred quiescent states.  This
commit therefore updates the checks in rcu_preempt_need_deferred_qs()
to allow exiting critical sections to report deferred quiescent states.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree_plugin.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 542791361908..24c209676d20 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -602,7 +602,7 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
 {
 	return (this_cpu_ptr(&rcu_preempt_data)->deferred_qs ||
 		READ_ONCE(t->rcu_read_unlock_special.s)) &&
-	       !t->rcu_read_lock_nesting;
+	       t->rcu_read_lock_nesting <= 0;
 }
 
 /*
-- 
2.17.1