---

yaml
---
r: 164337
b: refs/heads/master
c: b0e165c
h: refs/heads/master
i:
  164335: fc4e6c9
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: bbe3eae8bb039b5ffd64a6e3d1a0deaa1f3cbae9
+refs/heads/master: b0e165c035b13e1074fa0b555318bd9cb7102558

trunk/kernel/rcutree.c

@@ -632,6 +632,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
 	/* Special-case the common single-level case. */
 	if (NUM_RCU_NODES == 1) {
 		rnp->qsmask = rnp->qsmaskinit;
+		rcu_preempt_check_blocked_tasks(rnp);
 		rnp->gpnum = rsp->gpnum;
 		rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
 		spin_unlock_irqrestore(&rnp->lock, flags);
@@ -665,6 +666,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
 	for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) {
 		spin_lock(&rnp_cur->lock);	/* irqs already disabled. */
 		rnp_cur->qsmask = rnp_cur->qsmaskinit;
+		rcu_preempt_check_blocked_tasks(rnp);
 		rnp->gpnum = rsp->gpnum;
 		spin_unlock(&rnp_cur->lock);	/* irqs already disabled. */
 	}

trunk/kernel/rcutree_plugin.h

@@ -86,6 +86,7 @@ static void rcu_preempt_qs(int cpu)
 
 	if (t->rcu_read_lock_nesting &&
 	    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
+		WARN_ON_ONCE(cpu != smp_processor_id());
 
 		/* Possibly blocking in an RCU read-side critical section. */
 		rdp = rcu_preempt_state.rda[cpu];
@@ -103,7 +104,11 @@ static void rcu_preempt_qs(int cpu)
 		 * state for the current grace period), then as long
 		 * as that task remains queued, the current grace period
 		 * cannot end.
+		 *
+		 * But first, note that the current CPU must still be
+		 * on line!
 		 */
+		WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
 		phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1);
 		list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);
 		smp_mb();  /* Ensure later ctxt swtch seen after above. */
@@ -258,6 +263,18 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
 
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 
+/*
+ * Check that the list of blocked tasks for the newly completed grace
+ * period is in fact empty.  It is a serious bug to complete a grace
+ * period that still has RCU readers blocked!  This function must be
+ * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
+ * must be held by the caller.
+ */
+static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
+{
+	WARN_ON_ONCE(!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]));
+}
+
 /*
  * Check for preempted RCU readers for the specified rcu_node structure.
  * If the caller needs a reliable answer, it must hold the rcu_node's
@@ -450,6 +467,14 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
 
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 
+/*
+ * Because there is no preemptable RCU, there can be no readers blocked,
+ * so there is no need to check for blocked tasks.
+ */
+static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
+{
+}
+
 /*
  * Because preemptable RCU does not exist, there are never any preempted
  * RCU readers.