1 files changed, 50 insertions, 18 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 14dc7dd00902..8aafbb80b8b0 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -68,6 +68,7 @@ struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
 DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
 static struct rcu_state *rcu_state = &rcu_preempt_state;
 
+static void rcu_read_unlock_special(struct task_struct *t);
 static int rcu_preempted_readers_exp(struct rcu_node *rnp);
 
 /*
@@ -147,7 +148,7 @@ static void rcu_preempt_note_context_switch(int cpu)
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
 
-	if (t->rcu_read_lock_nesting &&
+	if (t->rcu_read_lock_nesting > 0 &&
 	    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
 
 		/* Possibly blocking in an RCU read-side critical section. */
@@ -190,6 +191,14 @@ static void rcu_preempt_note_context_switch(int cpu)
 				rnp->gp_tasks = &t->rcu_node_entry;
 		}
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
+	} else if (t->rcu_read_lock_nesting < 0 &&
+		   t->rcu_read_unlock_special) {
+
+		/*
+		 * Complete exit from RCU read-side critical section on
+		 * behalf of preempted instance of __rcu_read_unlock().
+		 */
+		rcu_read_unlock_special(t);
 	}
 
 	/*
@@ -284,7 +293,7 @@ static struct list_head *rcu_next_node_entry(struct task_struct *t,
  * notify RCU core processing or task having blocked during the RCU
  * read-side critical section.
  */
-static void rcu_read_unlock_special(struct task_struct *t)
+static noinline void rcu_read_unlock_special(struct task_struct *t)
 {
 	int empty;
 	int empty_exp;
@@ -309,7 +318,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
 	}
 
 	/* Hardware IRQ handlers cannot block. */
-	if (in_irq()) {
+	if (in_irq() || in_serving_softirq()) {
 		local_irq_restore(flags);
 		return;
 	}
@@ -342,6 +351,11 @@ static void rcu_read_unlock_special(struct task_struct *t)
 #ifdef CONFIG_RCU_BOOST
 		if (&t->rcu_node_entry == rnp->boost_tasks)
 			rnp->boost_tasks = np;
+		/* Snapshot and clear ->rcu_boosted with rcu_node lock held. */
+		if (t->rcu_boosted) {
+			special |= RCU_READ_UNLOCK_BOOSTED;
+			t->rcu_boosted = 0;
+		}
 #endif /* #ifdef CONFIG_RCU_BOOST */
 		t->rcu_blocked_node = NULL;
 
@@ -358,7 +372,6 @@ static void rcu_read_unlock_special(struct task_struct *t)
 #ifdef CONFIG_RCU_BOOST
 		/* Unboost if we were boosted. */
 		if (special & RCU_READ_UNLOCK_BOOSTED) {
-			t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED;
 			rt_mutex_unlock(t->rcu_boost_mutex);
 			t->rcu_boost_mutex = NULL;
 		}
@@ -387,13 +400,22 @@ void __rcu_read_unlock(void)
 	struct task_struct *t = current;
 
 	barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
-	--t->rcu_read_lock_nesting;
-	barrier();  /* decrement before load of ->rcu_read_unlock_special */
-	if (t->rcu_read_lock_nesting == 0 &&
-	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
-		rcu_read_unlock_special(t);
+	if (t->rcu_read_lock_nesting != 1)
+		--t->rcu_read_lock_nesting;
+	else {
+		t->rcu_read_lock_nesting = INT_MIN;
+		barrier();  /* assign before ->rcu_read_unlock_special load */
+		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
+			rcu_read_unlock_special(t);
+		barrier();  /* ->rcu_read_unlock_special load before assign */
+		t->rcu_read_lock_nesting = 0;
+	}
 #ifdef CONFIG_PROVE_LOCKING
-	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
+	{
+		int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
+
+		WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
+	}
 #endif /* #ifdef CONFIG_PROVE_LOCKING */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
@@ -589,7 +611,8 @@ static void rcu_preempt_check_callbacks(int cpu)
 		rcu_preempt_qs(cpu);
 		return;
 	}
-	if (per_cpu(rcu_preempt_data, cpu).qs_pending)
+	if (t->rcu_read_lock_nesting > 0 &&
+	    per_cpu(rcu_preempt_data, cpu).qs_pending)
 		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
 }
 
@@ -695,9 +718,12 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
 
 	raw_spin_lock_irqsave(&rnp->lock, flags);
 	for (;;) {
-		if (!sync_rcu_preempt_exp_done(rnp))
+		if (!sync_rcu_preempt_exp_done(rnp)) {
+			raw_spin_unlock_irqrestore(&rnp->lock, flags);
 			break;
+		}
 		if (rnp->parent == NULL) {
+			raw_spin_unlock_irqrestore(&rnp->lock, flags);
 			wake_up(&sync_rcu_preempt_exp_wq);
 			break;
 		}
@@ -707,7 +733,6 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
 		raw_spin_lock(&rnp->lock); /* irqs already disabled */
 		rnp->expmask &= ~mask;
 	}
-	raw_spin_unlock_irqrestore(&rnp->lock, flags);
 }
 
 /*
@@ -1174,7 +1199,7 @@ static int rcu_boost(struct rcu_node *rnp)
 	t = container_of(tb, struct task_struct, rcu_node_entry);
 	rt_mutex_init_proxy_locked(&mtx, t);
 	t->rcu_boost_mutex = &mtx;
-	t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED;
+	t->rcu_boosted = 1;
 	raw_spin_unlock_irqrestore(&rnp->lock, flags);
 	rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
 	rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
@@ -1532,7 +1557,7 @@ static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
 	struct sched_param sp;
 	struct task_struct *t;
 
-	if (!rcu_kthreads_spawnable ||
+	if (!rcu_scheduler_fully_active ||
 	    per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
 		return 0;
 	t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
@@ -1639,7 +1664,7 @@ static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
 	struct sched_param sp;
 	struct task_struct *t;
 
-	if (!rcu_kthreads_spawnable ||
+	if (!rcu_scheduler_fully_active ||
 	    rnp->qsmaskinit == 0)
 		return 0;
 	if (rnp->node_kthread_task == NULL) {
@@ -1665,7 +1690,7 @@ static int __init rcu_spawn_kthreads(void)
 	int cpu;
 	struct rcu_node *rnp;
 
-	rcu_kthreads_spawnable = 1;
+	rcu_scheduler_fully_active = 1;
 	for_each_possible_cpu(cpu) {
 		per_cpu(rcu_cpu_has_work, cpu) = 0;
 		if (cpu_online(cpu))
@@ -1687,7 +1712,7 @@ static void __cpuinit rcu_prepare_kthreads(int cpu)
 	struct rcu_node *rnp = rdp->mynode;
 
 	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
-	if (rcu_kthreads_spawnable) {
+	if (rcu_scheduler_fully_active) {
 		(void)rcu_spawn_one_cpu_kthread(cpu);
 		if (rnp->node_kthread_task == NULL)
 			(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
@@ -1726,6 +1751,13 @@ static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
 {
 }
 
+static int __init rcu_scheduler_really_started(void)
+{
+	rcu_scheduler_fully_active = 1;
+	return 0;
+}
+early_initcall(rcu_scheduler_really_started);
+
 static void __cpuinit rcu_prepare_kthreads(int cpu)
 {
 }