3 files changed, 75 insertions, 11 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 0f4a6a3c057b..da6f5213fb74 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -649,7 +649,6 @@ static noinstr void rcu_eqs_enter(bool user)
 	trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks));
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
 	rdp = this_cpu_ptr(&rcu_data);
-	do_nocb_deferred_wakeup(rdp);
 	rcu_prepare_for_idle();
 	rcu_preempt_deferred_qs(current);
 
@@ -683,6 +682,50 @@ void rcu_idle_enter(void)
 EXPORT_SYMBOL_GPL(rcu_idle_enter);
 
 #ifdef CONFIG_NO_HZ_FULL
+
+#if !defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)
+/*
+ * An empty function that will trigger a reschedule on
+ * IRQ tail once IRQs get re-enabled on userspace/guest resume.
+ */
+static void late_wakeup_func(struct irq_work *work)
+{
+}
+
+static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) =
+	IRQ_WORK_INIT(late_wakeup_func);
+
+/*
+ * If either:
+ *
+ * 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work
+ * 2) the task is about to enter in user mode and $ARCH doesn't support generic entry.
+ *
+ * In these cases the late RCU wake ups aren't supported in the resched loops and our
+ * last resort is to fire a local irq_work that will trigger a reschedule once IRQs
+ * get re-enabled again.
+ */
+noinstr static void rcu_irq_work_resched(void)
+{
+	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+
+	if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU))
+		return;
+
+	if (IS_ENABLED(CONFIG_KVM_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU))
+		return;
+
+	instrumentation_begin();
+	if (do_nocb_deferred_wakeup(rdp) && need_resched()) {
+		irq_work_queue(this_cpu_ptr(&late_wakeup_work));
+	}
+	instrumentation_end();
+}
+
+#else
+static inline void rcu_irq_work_resched(void) { }
+#endif
+
 /**
  * rcu_user_enter - inform RCU that we are resuming userspace.
  *
@@ -697,8 +740,16 @@ EXPORT_SYMBOL_GPL(rcu_idle_enter);
 noinstr void rcu_user_enter(void)
 {
 	lockdep_assert_irqs_disabled();
+
+	/*
+	 * Other than generic entry implementation, we may be past the last
+	 * rescheduling opportunity in the entry code. Trigger a self IPI
+	 * that will fire and reschedule once we resume in user/guest mode.
+	 */
+	rcu_irq_work_resched();
 	rcu_eqs_enter(true);
 }
+
 #endif /* CONFIG_NO_HZ_FULL */
 
 /**
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 5d359b9f9fec..71821d59d95c 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -435,7 +435,7 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
 				 unsigned long flags);
 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp);
-static void do_nocb_deferred_wakeup(struct rcu_data *rdp);
+static bool do_nocb_deferred_wakeup(struct rcu_data *rdp);
 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
 static void rcu_spawn_cpu_nocb_kthread(int cpu);
 static void __init rcu_spawn_nocb_kthreads(void);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 231a0c6cf03c..2d603771c7dc 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1632,8 +1632,8 @@ bool rcu_is_nocb_cpu(int cpu)
  * Kick the GP kthread for this NOCB group.  Caller holds ->nocb_lock
  * and this function releases it.
  */
-static void wake_nocb_gp(struct rcu_data *rdp, bool force,
-			   unsigned long flags)
+static bool wake_nocb_gp(struct rcu_data *rdp, bool force,
+			 unsigned long flags)
 	__releases(rdp->nocb_lock)
 {
 	bool needwake = false;
@@ -1644,7 +1644,7 @@ static void wake_nocb_gp(struct rcu_data *rdp, bool force,
 		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
 				    TPS("AlreadyAwake"));
 		rcu_nocb_unlock_irqrestore(rdp, flags);
-		return;
+		return false;
 	}
 	del_timer(&rdp->nocb_timer);
 	rcu_nocb_unlock_irqrestore(rdp, flags);
@@ -1657,6 +1657,8 @@ static void wake_nocb_gp(struct rcu_data *rdp, bool force,
 	raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
 	if (needwake)
 		wake_up_process(rdp_gp->nocb_gp_kthread);
+
+	return needwake;
 }
 
 /*
@@ -2251,20 +2253,23 @@ static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
 }
 
 /* Do a deferred wakeup of rcu_nocb_kthread(). */
-static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
+static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
 {
 	unsigned long flags;
 	int ndw;
+	int ret;
 
 	rcu_nocb_lock_irqsave(rdp, flags);
 	if (!rcu_nocb_need_deferred_wakeup(rdp)) {
 		rcu_nocb_unlock_irqrestore(rdp, flags);
-		return;
+		return false;
 	}
 	ndw = READ_ONCE(rdp->nocb_defer_wakeup);
 	WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
-	wake_nocb_gp(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
+	ret = wake_nocb_gp(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
 	trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake"));
+
+	return ret;
 }
 
 /* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
@@ -2280,11 +2285,18 @@ static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
  * This means we do an inexact common-case check.  Note that if
  * we miss, ->nocb_timer will eventually clean things up.
  */
-static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
+static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
 {
 	if (rcu_nocb_need_deferred_wakeup(rdp))
-		do_nocb_deferred_wakeup_common(rdp);
+		return do_nocb_deferred_wakeup_common(rdp);
+	return false;
+}
+
+void rcu_nocb_flush_deferred_wakeup(void)
+{
+	do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
 }
+EXPORT_SYMBOL_GPL(rcu_nocb_flush_deferred_wakeup);
 
 static int rdp_offload_toggle(struct rcu_data *rdp,
 			       bool offload, unsigned long flags)
@@ -2835,8 +2847,9 @@ static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
 	return false;
 }
 
-static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
+static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
 {
+	return false;
 }
 
 static void rcu_spawn_cpu_nocb_kthread(int cpu)