1 files changed, 109 insertions, 6 deletions

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 0f70f62039a9..be667583a554 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -18,6 +18,7 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp);
 static void rcu_exp_gp_seq_start(void)
 {
 	rcu_seq_start(&rcu_state.expedited_sequence);
+	rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
 }
 
 /*
@@ -34,6 +35,7 @@ static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void)
  */
 static void rcu_exp_gp_seq_end(void)
 {
+	rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
 	rcu_seq_end(&rcu_state.expedited_sequence);
 	smp_mb(); /* Ensure that consecutive grace periods serialize. */
 }
@@ -356,7 +358,7 @@ static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp)
 		    !(rnp->qsmaskinitnext & mask)) {
 			mask_ofl_test |= mask;
 		} else {
-			snap = rcu_dynticks_snap(rdp);
+			snap = rcu_dynticks_snap(cpu);
 			if (rcu_dynticks_in_eqs(snap))
 				mask_ofl_test |= mask;
 			else
@@ -621,7 +623,6 @@ static void synchronize_rcu_expedited_wait(void)
 			return;
 		if (rcu_stall_is_suppressed())
 			continue;
-		panic_on_rcu_stall();
 		trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
 		pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
 		       rcu_state.name);
@@ -636,10 +637,11 @@ static void synchronize_rcu_expedited_wait(void)
 					continue;
 				ndetected++;
 				rdp = per_cpu_ptr(&rcu_data, cpu);
-				pr_cont(" %d-%c%c%c", cpu,
+				pr_cont(" %d-%c%c%c%c", cpu,
 					"O."[!!cpu_online(cpu)],
 					"o."[!!(rdp->grpmask & rnp->expmaskinit)],
-					"N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
+					"N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
+					"D."[!!(rdp->cpu_no_qs.b.exp)]);
 			}
 		}
 		pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
@@ -669,6 +671,7 @@ static void synchronize_rcu_expedited_wait(void)
 			}
 		}
 		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
+		panic_on_rcu_stall();
 	}
 }
 
@@ -913,8 +916,18 @@ void synchronize_rcu_expedited(void)
 			 "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
 
 	/* Is the state is such that the call is a grace period? */
-	if (rcu_blocking_is_gp())
-		return;
+	if (rcu_blocking_is_gp()) {
+		// Note well that this code runs with !PREEMPT && !SMP.
+		// In addition, all code that advances grace periods runs
+		// at process level.  Therefore, this expedited GP overlaps
+		// with other expedited GPs only by being fully nested within
+		// them, which allows reuse of ->gp_seq_polled_exp_snap.
+		rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
+		rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
+		if (rcu_init_invoked())
+			cond_resched();
+		return;  // Context allows vacuous grace periods.
+	}
 
 	/* If expedited grace periods are prohibited, fall back to normal. */
 	if (rcu_gp_is_normal()) {
@@ -950,3 +963,93 @@ void synchronize_rcu_expedited(void)
 		synchronize_rcu_expedited_destroy_work(&rew);
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+/*
+ * Ensure that start_poll_synchronize_rcu_expedited() has the expedited
+ * RCU grace periods that it needs.
+ */
+static void sync_rcu_do_polled_gp(struct work_struct *wp)
+{
+	unsigned long flags;
+	int i = 0;
+	struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq);
+	unsigned long s;
+
+	raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
+	s = rnp->exp_seq_poll_rq;
+	rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
+	raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
+	if (s == RCU_GET_STATE_COMPLETED)
+		return;
+	while (!poll_state_synchronize_rcu(s)) {
+		synchronize_rcu_expedited();
+		if (i == 10 || i == 20)
+			pr_info("%s: i = %d s = %lx gp_seq_polled = %lx\n", __func__, i, s, READ_ONCE(rcu_state.gp_seq_polled));
+		i++;
+	}
+	raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
+	s = rnp->exp_seq_poll_rq;
+	if (poll_state_synchronize_rcu(s))
+		rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
+	raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
+}
+
+/**
+ * start_poll_synchronize_rcu_expedited - Snapshot current RCU state and start expedited grace period
+ *
+ * Returns a cookie to pass to a call to cond_synchronize_rcu(),
+ * cond_synchronize_rcu_expedited(), or poll_state_synchronize_rcu(),
+ * allowing them to determine whether or not any sort of grace period has
+ * elapsed in the meantime.  If the needed expedited grace period is not
+ * already slated to start, initiates that grace period.
+ */
+unsigned long start_poll_synchronize_rcu_expedited(void)
+{
+	unsigned long flags;
+	struct rcu_data *rdp;
+	struct rcu_node *rnp;
+	unsigned long s;
+
+	s = get_state_synchronize_rcu();
+	rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
+	rnp = rdp->mynode;
+	if (rcu_init_invoked())
+		raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
+	if (!poll_state_synchronize_rcu(s)) {
+		rnp->exp_seq_poll_rq = s;
+		if (rcu_init_invoked())
+			queue_work(rcu_gp_wq, &rnp->exp_poll_wq);
+	}
+	if (rcu_init_invoked())
+		raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
+
+	return s;
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited);
+
+/**
+ * cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period
+ *
+ * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
+ *
+ * If any type of full RCU grace period has elapsed since the earlier
+ * call to get_state_synchronize_rcu(), start_poll_synchronize_rcu(),
+ * or start_poll_synchronize_rcu_expedited(), just return.  Otherwise,
+ * invoke synchronize_rcu_expedited() to wait for a full grace period.
+ *
+ * Yes, this function does not take counter wrap into account.
+ * But counter wrap is harmless.  If the counter wraps, we have waited for
+ * more than 2 billion grace periods (and way more on a 64-bit system!),
+ * so waiting for a couple of additional grace periods should be just fine.
+ *
+ * This function provides the same memory-ordering guarantees that
+ * would be provided by a synchronize_rcu() that was invoked at the call
+ * to the function that provided @oldstate and that returned at the end
+ * of this function.
+ */
+void cond_synchronize_rcu_expedited(unsigned long oldstate)
+{
+	if (!poll_state_synchronize_rcu(oldstate))
+		synchronize_rcu_expedited();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);