rcu: Inline _rcu_barrier() into its sole remaining caller

Because rcu_barrier() is a one-line wrapper function for _rcu_barrier()
and because nothing else calls _rcu_barrier(), this commit inlines
_rcu_barrier() into rcu_barrier().
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

include/trace/events/rcu.h

@@ -705,20 +705,20 @@ TRACE_EVENT(rcu_torture_read,
 );
 
 /*
- * Tracepoint for _rcu_barrier() execution.  The string "s" describes
- * the _rcu_barrier phase:
- *	"Begin": _rcu_barrier() started.
- *	"EarlyExit": _rcu_barrier() piggybacked, thus early exit.
- *	"Inc1": _rcu_barrier() piggyback check counter incremented.
- *	"OfflineNoCB": _rcu_barrier() found callback on never-online CPU
- *	"OnlineNoCB": _rcu_barrier() found online no-CBs CPU.
- *	"OnlineQ": _rcu_barrier() found online CPU with callbacks.
- *	"OnlineNQ": _rcu_barrier() found online CPU, no callbacks.
+ * Tracepoint for rcu_barrier() execution.  The string "s" describes
+ * the rcu_barrier phase:
+ *	"Begin": rcu_barrier() started.
+ *	"EarlyExit": rcu_barrier() piggybacked, thus early exit.
+ *	"Inc1": rcu_barrier() piggyback check counter incremented.
+ *	"OfflineNoCB": rcu_barrier() found callback on never-online CPU
+ *	"OnlineNoCB": rcu_barrier() found online no-CBs CPU.
+ *	"OnlineQ": rcu_barrier() found online CPU with callbacks.
+ *	"OnlineNQ": rcu_barrier() found online CPU, no callbacks.
  *	"IRQ": An rcu_barrier_callback() callback posted on remote CPU.
  *	"IRQNQ": An rcu_barrier_callback() callback found no callbacks.
  *	"CB": An rcu_barrier_callback() invoked a callback, not the last.
  *	"LastCB": An rcu_barrier_callback() invoked the last callback.
- *	"Inc2": _rcu_barrier() piggyback check counter incremented.
+ *	"Inc2": rcu_barrier() piggyback check counter incremented.
  * The "cpu" argument is the CPU or -1 if meaningless, the "cnt" argument
  * is the count of remaining callbacks, and "done" is the piggybacking count.
  */

kernel/rcu/tree.c

@@ -2747,7 +2747,7 @@ static void rcu_leak_callback(struct rcu_head *rhp)
 /*
  * Helper function for call_rcu() and friends.  The cpu argument will
  * normally be -1, indicating "currently running CPU".  It may specify
- * a CPU only if that CPU is a no-CBs CPU.  Currently, only _rcu_barrier()
+ * a CPU only if that CPU is a no-CBs CPU.  Currently, only rcu_barrier()
  * is expected to specify a CPU.
  */
 static void
@@ -2981,27 +2981,27 @@ static bool rcu_cpu_has_callbacks(bool *all_lazy)
 }
 
 /*
- * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
+ * Helper function for rcu_barrier() tracing.  If tracing is disabled,
  * the compiler is expected to optimize this away.
  */
-static void _rcu_barrier_trace(const char *s, int cpu, unsigned long done)
+static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
 {
 	trace_rcu_barrier(rcu_state.name, s, cpu,
 			  atomic_read(&rcu_state.barrier_cpu_count), done);
 }
 
 /*
- * RCU callback function for _rcu_barrier().  If we are last, wake
- * up the task executing _rcu_barrier().
+ * RCU callback function for rcu_barrier().  If we are last, wake
+ * up the task executing rcu_barrier().
  */
 static void rcu_barrier_callback(struct rcu_head *rhp)
 {
 	if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
-		_rcu_barrier_trace(TPS("LastCB"), -1,
+		rcu_barrier_trace(TPS("LastCB"), -1,
 				   rcu_state.barrier_sequence);
 		complete(&rcu_state.barrier_completion);
 	} else {
-		_rcu_barrier_trace(TPS("CB"), -1, rcu_state.barrier_sequence);
+		rcu_barrier_trace(TPS("CB"), -1, rcu_state.barrier_sequence);
 	}
 }
 
@@ -3012,33 +3012,40 @@ static void rcu_barrier_func(void *unused)
 {
 	struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
 
-	_rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.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(&rcu_state.barrier_cpu_count);
 	} else {
 		debug_rcu_head_unqueue(&rdp->barrier_head);
-		_rcu_barrier_trace(TPS("IRQNQ"), -1,
+		rcu_barrier_trace(TPS("IRQNQ"), -1,
 				   rcu_state.barrier_sequence);
 	}
 }
 
-/* Orchestrate an RCU barrier, waiting for all RCU callbacks to complete.  */
-static void _rcu_barrier(void)
+/**
+ * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
+ *
+ * Note that this primitive does not necessarily wait for an RCU grace period
+ * to complete.  For example, if there are no RCU callbacks queued anywhere
+ * in the system, then rcu_barrier() is within its rights to return
+ * immediately, without waiting for anything, much less an RCU grace period.
+ */
+void rcu_barrier(void)
 {
 	int cpu;
 	struct rcu_data *rdp;
 	unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
 
-	_rcu_barrier_trace(TPS("Begin"), -1, s);
+	rcu_barrier_trace(TPS("Begin"), -1, s);
 
 	/* Take mutex to serialize concurrent rcu_barrier() requests. */
 	mutex_lock(&rcu_state.barrier_mutex);
 
 	/* Did someone else do our work for us? */
 	if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
-		_rcu_barrier_trace(TPS("EarlyExit"), -1,
+		rcu_barrier_trace(TPS("EarlyExit"), -1,
 				   rcu_state.barrier_sequence);
 		smp_mb(); /* caller's subsequent code after above check. */
 		mutex_unlock(&rcu_state.barrier_mutex);
@@ -3047,7 +3054,7 @@ static void _rcu_barrier(void)
 
 	/* Mark the start of the barrier operation. */
 	rcu_seq_start(&rcu_state.barrier_sequence);
-	_rcu_barrier_trace(TPS("Inc1"), -1, 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
@@ -3070,10 +3077,10 @@ static void _rcu_barrier(void)
 		rdp = per_cpu_ptr(&rcu_data, cpu);
 		if (rcu_is_nocb_cpu(cpu)) {
 			if (!rcu_nocb_cpu_needs_barrier(cpu)) {
-				_rcu_barrier_trace(TPS("OfflineNoCB"), cpu,
+				rcu_barrier_trace(TPS("OfflineNoCB"), cpu,
 						   rcu_state.barrier_sequence);
 			} else {
-				_rcu_barrier_trace(TPS("OnlineNoCB"), cpu,
+				rcu_barrier_trace(TPS("OnlineNoCB"), cpu,
 						   rcu_state.barrier_sequence);
 				smp_mb__before_atomic();
 				atomic_inc(&rcu_state.barrier_cpu_count);
@@ -3081,11 +3088,11 @@ static void _rcu_barrier(void)
 					   rcu_barrier_callback, cpu, 0);
 			}
 		} else if (rcu_segcblist_n_cbs(&rdp->cblist)) {
-			_rcu_barrier_trace(TPS("OnlineQ"), cpu,
+			rcu_barrier_trace(TPS("OnlineQ"), cpu,
 					   rcu_state.barrier_sequence);
 			smp_call_function_single(cpu, rcu_barrier_func, NULL, 1);
 		} else {
-			_rcu_barrier_trace(TPS("OnlineNQ"), cpu,
+			rcu_barrier_trace(TPS("OnlineNQ"), cpu,
 					   rcu_state.barrier_sequence);
 		}
 	}
@@ -3102,25 +3109,12 @@ static void _rcu_barrier(void)
 	wait_for_completion(&rcu_state.barrier_completion);
 
 	/* Mark the end of the barrier operation. */
-	_rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.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(&rcu_state.barrier_mutex);
 }
-
-/**
- * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
- *
- * Note that this primitive does not necessarily wait for an RCU grace period
- * to complete.  For example, if there are no RCU callbacks queued anywhere
- * in the system, then rcu_barrier() is within its rights to return
- * immediately, without waiting for anything, much less an RCU grace period.
- */
-void rcu_barrier(void)
-{
-	_rcu_barrier();
-}
 EXPORT_SYMBOL_GPL(rcu_barrier);
 
 /*

kernel/rcu/tree.h

@@ -222,7 +222,7 @@ struct rcu_data {
 					/* Grace period that needs help */
 					/*  from cond_resched(). */
 
-	/* 5) _rcu_barrier(), OOM callbacks, and expediting. */
+	/* 5) rcu_barrier(), OOM callbacks, and expediting. */
 	struct rcu_head barrier_head;
 	int exp_dynticks_snap;		/* Double-check need for IPI. */
 
@@ -328,7 +328,7 @@ struct rcu_state {
 	atomic_t barrier_cpu_count;		/* # CPUs waiting on. */
 	struct completion barrier_completion;	/* Wake at barrier end. */
 	unsigned long barrier_sequence;		/* ++ at start and end of */
-						/*  _rcu_barrier(). */
+						/*  rcu_barrier(). */
 	/* End of fields guarded by barrier_mutex. */
 
 	struct mutex exp_mutex;			/* Serialize expedited GP. */

kernel/rcu/tree_plugin.h

@@ -1993,7 +1993,7 @@ static bool rcu_nocb_cpu_needs_barrier(int cpu)
 	 * There needs to be a barrier before this function is called,
 	 * but associated with a prior determination that no more
 	 * callbacks would be posted.  In the worst case, the first
-	 * barrier in _rcu_barrier() suffices (but the caller cannot
+	 * barrier in rcu_barrier() suffices (but the caller cannot
 	 * necessarily rely on this, not a substitute for the caller
 	 * getting the concurrency design right!).  There must also be
 	 * a barrier between the following load an posting of a callback