rcu: Move irq-disabled stall-warning checking to tree_stall.h

The rcu_iw_handler() function's sole purpose in life is to indicate
whether a stalled CPU had interrupts disabled, so it belongs in
kernel/rcu/tree_stall.h.  This commit therefore makes that move,
clarifying its header comment while in the area.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

kernel/rcu/tree.c

@@ -1031,27 +1031,6 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp)
 	return 0;
 }
 
-/*
- * Handler for the irq_work request posted when a grace period has
- * gone on for too long, but not yet long enough for an RCU CPU
- * stall warning.  Set state appropriately, but just complain if
- * there is unexpected state on entry.
- */
-static void rcu_iw_handler(struct irq_work *iwp)
-{
-	struct rcu_data *rdp;
-	struct rcu_node *rnp;
-
-	rdp = container_of(iwp, struct rcu_data, rcu_iw);
-	rnp = rdp->mynode;
-	raw_spin_lock_rcu_node(rnp);
-	if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
-		rdp->rcu_iw_gp_seq = rnp->gp_seq;
-		rdp->rcu_iw_pending = false;
-	}
-	raw_spin_unlock_rcu_node(rnp);
-}
-
 /*
  * Return true if the specified CPU has passed through a quiescent
  * state by virtue of being in or having passed through an dynticks

kernel/rcu/tree.h

@@ -443,4 +443,5 @@ static void rcu_dynticks_task_exit(void);
 
 /* Forward declarations for tree_stall.h */
 static void record_gp_stall_check_time(void);
+static void rcu_iw_handler(struct irq_work *iwp);
 static void check_cpu_stall(struct rcu_data *rdp);

kernel/rcu/tree_stall.h

@@ -139,6 +139,26 @@ static void rcu_stall_kick_kthreads(void)
 	}
 }
 
+/*
+ * Handler for the irq_work request posted about halfway into the RCU CPU
+ * stall timeout, and used to detect excessive irq disabling.  Set state
+ * appropriately, but just complain if there is unexpected state on entry.
+ */
+static void rcu_iw_handler(struct irq_work *iwp)
+{
+	struct rcu_data *rdp;
+	struct rcu_node *rnp;
+
+	rdp = container_of(iwp, struct rcu_data, rcu_iw);
+	rnp = rdp->mynode;
+	raw_spin_lock_rcu_node(rnp);
+	if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
+		rdp->rcu_iw_gp_seq = rnp->gp_seq;
+		rdp->rcu_iw_pending = false;
+	}
+	raw_spin_unlock_rcu_node(rnp);
+}
+
 //////////////////////////////////////////////////////////////////////////////
 //
 // Printing RCU CPU stall warnings