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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 50/52] rcu: Eliminate RCU-barrier use of rsp
Date:   Wed, 29 Aug 2018 15:38:52 -0700
In-Reply-To: <20180829223830.GA1800@linux.vnet.ibm.com>
References: <20180829223830.GA1800@linux.vnet.ibm.com>
Message-Id: <20180829223854.4055-50-paulmck@linux.vnet.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Now that there is only one rcu_state structure, there is less point
in maintaining a pointer to it.  This commit therefore replaces rsp
with &rcu_state in rcu_barrier_callback(), rcu_barrier_func(), and
_rcu_barrier().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 65 +++++++++++++++++++++++------------------------
 1 file changed, 32 insertions(+), 33 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 962b75c9722a..e573fb9f0ef8 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3128,32 +3128,31 @@ static void _rcu_barrier_trace(const char *s, int cpu, unsigned long done)
  */
 static void rcu_barrier_callback(struct rcu_head *rhp)
 {
-	struct rcu_state *rsp = &rcu_state;
-
-	if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
-		_rcu_barrier_trace(TPS("LastCB"), -1, rsp->barrier_sequence);
-		complete(&rsp->barrier_completion);
+	if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
+		_rcu_barrier_trace(TPS("LastCB"), -1,
+				   rcu_state.barrier_sequence);
+		complete(&rcu_state.barrier_completion);
 	} else {
-		_rcu_barrier_trace(TPS("CB"), -1, rsp->barrier_sequence);
+		_rcu_barrier_trace(TPS("CB"), -1, rcu_state.barrier_sequence);
 	}
 }
 
 /*
  * Called with preemption disabled, and from cross-cpu IRQ context.
  */
-static void rcu_barrier_func(void *type)
+static void rcu_barrier_func(void *unused)
 {
-	struct rcu_state *rsp = type;
 	struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
 
-	_rcu_barrier_trace(TPS("IRQ"), -1, rsp->barrier_sequence);
+	_rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
 	rdp->barrier_head.func = rcu_barrier_callback;
 	debug_rcu_head_queue(&rdp->barrier_head);
 	if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head, 0)) {
-		atomic_inc(&rsp->barrier_cpu_count);
+		atomic_inc(&rcu_state.barrier_cpu_count);
 	} else {
 		debug_rcu_head_unqueue(&rdp->barrier_head);
-		_rcu_barrier_trace(TPS("IRQNQ"), -1, rsp->barrier_sequence);
+		_rcu_barrier_trace(TPS("IRQNQ"), -1,
+				   rcu_state.barrier_sequence);
 	}
 }
 
@@ -3165,25 +3164,25 @@ static void _rcu_barrier(void)
 {
 	int cpu;
 	struct rcu_data *rdp;
-	struct rcu_state *rsp = &rcu_state;
-	unsigned long s = rcu_seq_snap(&rsp->barrier_sequence);
+	unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
 
 	_rcu_barrier_trace(TPS("Begin"), -1, s);
 
 	/* Take mutex to serialize concurrent rcu_barrier() requests. */
-	mutex_lock(&rsp->barrier_mutex);
+	mutex_lock(&rcu_state.barrier_mutex);
 
 	/* Did someone else do our work for us? */
-	if (rcu_seq_done(&rsp->barrier_sequence, s)) {
-		_rcu_barrier_trace(TPS("EarlyExit"), -1, rsp->barrier_sequence);
+	if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
+		_rcu_barrier_trace(TPS("EarlyExit"), -1,
+				   rcu_state.barrier_sequence);
 		smp_mb(); /* caller's subsequent code after above check. */
-		mutex_unlock(&rsp->barrier_mutex);
+		mutex_unlock(&rcu_state.barrier_mutex);
 		return;
 	}
 
 	/* Mark the start of the barrier operation. */
-	rcu_seq_start(&rsp->barrier_sequence);
-	_rcu_barrier_trace(TPS("Inc1"), -1, rsp->barrier_sequence);
+	rcu_seq_start(&rcu_state.barrier_sequence);
+	_rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
 
 	/*
 	 * Initialize the count to one rather than to zero in order to
@@ -3191,8 +3190,8 @@ static void _rcu_barrier(void)
 	 * (or preemption of this task).  Exclude CPU-hotplug operations
 	 * to ensure that no offline CPU has callbacks queued.
 	 */
-	init_completion(&rsp->barrier_completion);
-	atomic_set(&rsp->barrier_cpu_count, 1);
+	init_completion(&rcu_state.barrier_completion);
+	atomic_set(&rcu_state.barrier_cpu_count, 1);
 	get_online_cpus();
 
 	/*
@@ -3207,22 +3206,22 @@ static void _rcu_barrier(void)
 		if (rcu_is_nocb_cpu(cpu)) {
 			if (!rcu_nocb_cpu_needs_barrier(cpu)) {
 				_rcu_barrier_trace(TPS("OfflineNoCB"), cpu,
-						   rsp->barrier_sequence);
+						   rcu_state.barrier_sequence);
 			} else {
 				_rcu_barrier_trace(TPS("OnlineNoCB"), cpu,
-						   rsp->barrier_sequence);
+						   rcu_state.barrier_sequence);
 				smp_mb__before_atomic();
-				atomic_inc(&rsp->barrier_cpu_count);
+				atomic_inc(&rcu_state.barrier_cpu_count);
 				__call_rcu(&rdp->barrier_head,
 					   rcu_barrier_callback, cpu, 0);
 			}
 		} else if (rcu_segcblist_n_cbs(&rdp->cblist)) {
 			_rcu_barrier_trace(TPS("OnlineQ"), cpu,
-					   rsp->barrier_sequence);
-			smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
+					   rcu_state.barrier_sequence);
+			smp_call_function_single(cpu, rcu_barrier_func, NULL, 1);
 		} else {
 			_rcu_barrier_trace(TPS("OnlineNQ"), cpu,
-					   rsp->barrier_sequence);
+					   rcu_state.barrier_sequence);
 		}
 	}
 	put_online_cpus();
@@ -3231,18 +3230,18 @@ static void _rcu_barrier(void)
 	 * Now that we have an rcu_barrier_callback() callback on each
 	 * CPU, and thus each counted, remove the initial count.
 	 */
-	if (atomic_dec_and_test(&rsp->barrier_cpu_count))
-		complete(&rsp->barrier_completion);
+	if (atomic_dec_and_test(&rcu_state.barrier_cpu_count))
+		complete(&rcu_state.barrier_completion);
 
 	/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
-	wait_for_completion(&rsp->barrier_completion);
+	wait_for_completion(&rcu_state.barrier_completion);
 
 	/* Mark the end of the barrier operation. */
-	_rcu_barrier_trace(TPS("Inc2"), -1, rsp->barrier_sequence);
-	rcu_seq_end(&rsp->barrier_sequence);
+	_rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
+	rcu_seq_end(&rcu_state.barrier_sequence);
 
 	/* Other rcu_barrier() invocations can now safely proceed. */
-	mutex_unlock(&rsp->barrier_mutex);
+	mutex_unlock(&rcu_state.barrier_mutex);
 }
 
 /**
-- 
2.17.1