1 files changed, 33 insertions, 0 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 387dd4599344..c1d7f27bd38f 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2050,6 +2050,33 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force)
 }
 
 /*
+ * Does the specified CPU need an RCU callback for the specified flavor
+ * of rcu_barrier()?
+ */
+static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
+{
+        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+        struct rcu_head *rhp;
+
+        /* No-CBs CPUs might have callbacks on any of three lists. */
+        rhp = ACCESS_ONCE(rdp->nocb_head);
+        if (!rhp)
+                rhp = ACCESS_ONCE(rdp->nocb_gp_head);
+        if (!rhp)
+                rhp = ACCESS_ONCE(rdp->nocb_follower_head);
+
+        /* Having no rcuo kthread but CBs after scheduler starts is bad! */
+        if (!ACCESS_ONCE(rdp->nocb_kthread) && rhp) {
+                /* RCU callback enqueued before CPU first came online??? */
+                pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
+                       cpu, rhp->func);
+                WARN_ON_ONCE(1);
+        }
+
+        return !!rhp;
+}
+
+/*
  * Enqueue the specified string of rcu_head structures onto the specified
  * CPU's no-CBs lists.  The CPU is specified by rdp, the head of the
  * string by rhp, and the tail of the string by rhtp.  The non-lazy/lazy
@@ -2642,6 +2669,12 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
 
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 
+static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
+{
+        WARN_ON_ONCE(1); /* Should be dead code. */
+        return false;
+}
+
 static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
 {
 }