1 files changed, 31 insertions, 15 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 05915e536336..605ff3b06098 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -397,6 +397,11 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
 	return rnp->gp_tasks != NULL;
 }
 
+/* Bias and limit values for ->rcu_read_lock_nesting. */
+#define RCU_NEST_BIAS INT_MAX
+#define RCU_NEST_NMAX (-INT_MAX / 2)
+#define RCU_NEST_PMAX (INT_MAX / 2)
+
 /*
  * Preemptible RCU implementation for rcu_read_lock().
  * Just increment ->rcu_read_lock_nesting, shared state will be updated
@@ -405,6 +410,8 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
 void __rcu_read_lock(void)
 {
 	current->rcu_read_lock_nesting++;
+	if (IS_ENABLED(CONFIG_PROVE_LOCKING))
+		WARN_ON_ONCE(current->rcu_read_lock_nesting > RCU_NEST_PMAX);
 	barrier();  /* critical section after entry code. */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_lock);
@@ -424,20 +431,18 @@ void __rcu_read_unlock(void)
 		--t->rcu_read_lock_nesting;
 	} else {
 		barrier();  /* critical section before exit code. */
-		t->rcu_read_lock_nesting = INT_MIN;
+		t->rcu_read_lock_nesting = -RCU_NEST_BIAS;
 		barrier();  /* assign before ->rcu_read_unlock_special load */
 		if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
 			rcu_read_unlock_special(t);
 		barrier();  /* ->rcu_read_unlock_special load before assign */
 		t->rcu_read_lock_nesting = 0;
 	}
-#ifdef CONFIG_PROVE_LOCKING
-	{
-		int rrln = READ_ONCE(t->rcu_read_lock_nesting);
+	if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
+		int rrln = t->rcu_read_lock_nesting;
 
-		WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
+		WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX);
 	}
-#endif /* #ifdef CONFIG_PROVE_LOCKING */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 
@@ -597,7 +602,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
  */
 static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
 {
-	return (this_cpu_ptr(&rcu_data)->deferred_qs ||
+	return (__this_cpu_read(rcu_data.deferred_qs) ||
 		READ_ONCE(t->rcu_read_unlock_special.s)) &&
 	       t->rcu_read_lock_nesting <= 0;
 }
@@ -617,11 +622,11 @@ static void rcu_preempt_deferred_qs(struct task_struct *t)
 	if (!rcu_preempt_need_deferred_qs(t))
 		return;
 	if (couldrecurse)
-		t->rcu_read_lock_nesting -= INT_MIN;
+		t->rcu_read_lock_nesting -= RCU_NEST_BIAS;
 	local_irq_save(flags);
 	rcu_preempt_deferred_qs_irqrestore(t, flags);
 	if (couldrecurse)
-		t->rcu_read_lock_nesting += INT_MIN;
+		t->rcu_read_lock_nesting += RCU_NEST_BIAS;
 }
 
 /*
@@ -642,13 +647,21 @@ static void rcu_read_unlock_special(struct task_struct *t)
 
 	local_irq_save(flags);
 	irqs_were_disabled = irqs_disabled_flags(flags);
-	if ((preempt_bh_were_disabled || irqs_were_disabled) &&
-	    t->rcu_read_unlock_special.b.blocked) {
+	if (preempt_bh_were_disabled || irqs_were_disabled) {
+		WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false);
 		/* Need to defer quiescent state until everything is enabled. */
-		raise_softirq_irqoff(RCU_SOFTIRQ);
+		if (irqs_were_disabled) {
+			/* Enabling irqs does not reschedule, so... */
+			raise_softirq_irqoff(RCU_SOFTIRQ);
+		} else {
+			/* Enabling BH or preempt does reschedule, so... */
+			set_tsk_need_resched(current);
+			set_preempt_need_resched();
+		}
 		local_irq_restore(flags);
 		return;
 	}
+	WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false);
 	rcu_preempt_deferred_qs_irqrestore(t, flags);
 }
 
@@ -1464,7 +1477,8 @@ static void __init rcu_spawn_boost_kthreads(void)
 
 	for_each_possible_cpu(cpu)
 		per_cpu(rcu_cpu_has_work, cpu) = 0;
-	BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
+	if (WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcub kthread, OOM is now expected behavior\n", __func__))
+		return;
 	rcu_for_each_leaf_node(rnp)
 		(void)rcu_spawn_one_boost_kthread(rnp);
 }
@@ -2322,7 +2336,8 @@ static int rcu_nocb_kthread(void *arg)
 		tail = rdp->nocb_follower_tail;
 		rdp->nocb_follower_tail = &rdp->nocb_follower_head;
 		raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
-		BUG_ON(!list);
+		if (WARN_ON_ONCE(!list))
+			continue;
 		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeNonEmpty"));
 
 		/* Each pass through the following loop invokes a callback. */
@@ -2495,7 +2510,8 @@ static void rcu_spawn_one_nocb_kthread(int cpu)
 	/* Spawn the kthread for this CPU. */
 	t = kthread_run(rcu_nocb_kthread, rdp_spawn,
 			"rcuo%c/%d", rcu_state.abbr, cpu);
-	BUG_ON(IS_ERR(t));
+	if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo kthread, OOM is now expected behavior\n", __func__))
+		return;
 	WRITE_ONCE(rdp_spawn->nocb_kthread, t);
 }