[RFC,tip/core/rcu,2/6] rcu: Augment rcu_batch_end tracing for idle and callback state

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index c75418c..d2d88be 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -461,27 +461,46 @@  TRACE_EVENT(rcu_invoke_kfree_callback,
 
 /*
  * Tracepoint for exiting rcu_do_batch after RCU callbacks have been
- * invoked.  The first argument is the name of the RCU flavor and
- * the second argument is number of callbacks actually invoked.
+ * invoked.  The first argument is the name of the RCU flavor,
+ * the second argument is number of callbacks actually invoked,
+ * the third argument (cb) is whether or not any of the callbacks that
+ * were ready to invoke at the beginning of this batch are still
+ * queued, the fourth argument (nr) is the return value of need_resched(),
+ * the fifth argument (iit) is 1 if the current task is the idle task,
+ * and the sixth argument (risk) is the return value from
+ * rcu_is_callbacks_kthread().
  */
 TRACE_EVENT(rcu_batch_end,
 
-	TP_PROTO(char *rcuname, int callbacks_invoked),
+	TP_PROTO(char *rcuname, int callbacks_invoked,
+		 bool cb, bool nr, bool iit, bool risk),
 
-	TP_ARGS(rcuname, callbacks_invoked),
+	TP_ARGS(rcuname, callbacks_invoked, cb, nr, iit, risk),
 
 	TP_STRUCT__entry(
 		__field(char *, rcuname)
 		__field(int, callbacks_invoked)
+		__field(bool, cb)
+		__field(bool, nr)
+		__field(bool, iit)
+		__field(bool, risk)
 	),
 
 	TP_fast_assign(
 		__entry->rcuname = rcuname;
 		__entry->callbacks_invoked = callbacks_invoked;
-	),
-
-	TP_printk("%s CBs-invoked=%d",
-		  __entry->rcuname, __entry->callbacks_invoked)
+		__entry->cb = cb;
+		__entry->nr = nr;
+		__entry->iit = iit;
+		__entry->risk = risk;
+	),
+
+	TP_printk("%s CBs-invoked=%d idle=%c%c%c%c",
+		  __entry->rcuname, __entry->callbacks_invoked,
+		  __entry->cb ? 'C' : '.',
+		  __entry->nr ? 'S' : '.',
+		  __entry->iit ? 'I' : '.',
+		  __entry->risk ? 'R' : '.')
 );
 
 /*
@@ -524,7 +543,8 @@  TRACE_EVENT(rcu_torture_read,
 #define trace_rcu_batch_start(rcuname, qlen, blimit) do { } while (0)
 #define trace_rcu_invoke_callback(rcuname, rhp) do { } while (0)
 #define trace_rcu_invoke_kfree_callback(rcuname, rhp, offset) do { } while (0)
-#define trace_rcu_batch_end(rcuname, callbacks_invoked) do { } while (0)
+#define trace_rcu_batch_end(rcuname, callbacks_invoked, cb, nr, iit, risk) \
+	do { } while (0)
 #define trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
 
 #endif /* #else #ifdef CONFIG_RCU_TRACE */
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index e5bd949..977296d 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -259,7 +259,11 @@  static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 	/* If no RCU callbacks ready to invoke, just return. */
 	if (&rcp->rcucblist == rcp->donetail) {
 		RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
-		RCU_TRACE(trace_rcu_batch_end(rcp->name, 0));
+		RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
+					      ACCESS_ONCE(rcp->rcucblist),
+					      need_resched(),
+					      is_idle_task(current),
+					      rcu_is_callbacks_kthread()));
 		return;
 	}
 
@@ -288,7 +292,9 @@  static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 		RCU_TRACE(cb_count++);
 	}
 	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
-	RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count));
+	RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
+				      is_idle_task(current),
+				      rcu_is_callbacks_kthread()));
 }
 
 static void rcu_process_callbacks(struct softirq_action *unused)
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 2b0484a..dfa97cb 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -885,6 +885,19 @@  static void invoke_rcu_callbacks(void)
 	wake_up(&rcu_kthread_wq);
 }
 
+#ifdef CONFIG_RCU_TRACE
+
+/*
+ * Is the current CPU running the RCU-callbacks kthread?
+ * Caller must have preemption disabled.
+ */
+static bool rcu_is_callbacks_kthread(void)
+{
+	return rcu_kthread_task == current;
+}
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
+
 /*
  * This kthread invokes RCU callbacks whose grace periods have
  * elapsed.  It is awakened as needed, and takes the place of the
@@ -938,6 +951,18 @@  void invoke_rcu_callbacks(void)
 	raise_softirq(RCU_SOFTIRQ);
 }
 
+#ifdef CONFIG_RCU_TRACE
+
+/*
+ * There is no callback kthread, so this thread is never it.
+ */
+static bool rcu_is_callbacks_kthread(void)
+{
+	return false;
+}
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
+
 void rcu_init(void)
 {
 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 2b2e1a9..6c4a672 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1373,7 +1373,9 @@  static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 	/* If no callbacks are ready, just return.*/
 	if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
 		trace_rcu_batch_start(rsp->name, 0, 0);
-		trace_rcu_batch_end(rsp->name, 0);
+		trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
+				    need_resched(), is_idle_task(current),
+				    rcu_is_callbacks_kthread());
 		return;
 	}
 
@@ -1409,7 +1411,9 @@  static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 	}
 
 	local_irq_save(flags);
-	trace_rcu_batch_end(rsp->name, count);
+	trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
+			    is_idle_task(current),
+			    rcu_is_callbacks_kthread());
 
 	/* Update count, and requeue any remaining callbacks. */
 	rdp->qlen -= count;