1 files changed, 60 insertions, 17 deletions

diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 9cb1ae4aabdd..22ecea0dfb62 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -132,6 +132,7 @@ static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
         RCU_TRACE(.rcb.name = "rcu_preempt")
 };
 
+static void rcu_read_unlock_special(struct task_struct *t);
 static int rcu_preempted_readers_exp(void);
 static void rcu_report_exp_done(void);
 
@@ -146,6 +147,16 @@ static int rcu_cpu_blocking_cur_gp(void)
 /*
  * Check for a running RCU reader.  Because there is only one CPU,
  * there can be but one running RCU reader at a time.  ;-)
+ *
+ * Returns zero if there are no running readers.  Returns a positive
+ * number if there is at least one reader within its RCU read-side
+ * critical section.  Returns a negative number if an outermost reader
+ * is in the midst of exiting from its RCU read-side critical section
+ *
+ * Returns zero if there are no running readers.  Returns a positive
+ * number if there is at least one reader within its RCU read-side
+ * critical section.  Returns a negative number if an outermost reader
+ * is in the midst of exiting from its RCU read-side critical section.
  */
 static int rcu_preempt_running_reader(void)
 {
@@ -307,7 +318,6 @@ static int rcu_boost(void)
         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;
         raw_local_irq_restore(flags);
         rt_mutex_lock(&mtx);
         rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
@@ -475,7 +485,7 @@ void rcu_preempt_note_context_switch(void)
         unsigned long flags;
 
         local_irq_save(flags); /* must exclude scheduler_tick(). */
-        if (rcu_preempt_running_reader() &&
+        if (rcu_preempt_running_reader() > 0 &&
             (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
 
                 /* Possibly blocking in an RCU read-side critical section. */
@@ -494,6 +504,13 @@ void rcu_preempt_note_context_switch(void)
                 list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
                 if (rcu_cpu_blocking_cur_gp())
                         rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
+        } else if (rcu_preempt_running_reader() < 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);
         }
 
         /*
@@ -526,12 +543,15 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock);
  * 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;
         unsigned long flags;
         struct list_head *np;
+#ifdef CONFIG_RCU_BOOST
+        struct rt_mutex *rbmp = NULL;
+#endif /* #ifdef CONFIG_RCU_BOOST */
         int special;
 
         /*
@@ -552,7 +572,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
                 rcu_preempt_cpu_qs();
 
         /* Hardware IRQ handlers cannot block. */
-        if (in_irq()) {
+        if (in_irq() || in_serving_softirq()) {
                 local_irq_restore(flags);
                 return;
         }
@@ -597,10 +617,10 @@ static void rcu_read_unlock_special(struct task_struct *t)
         }
 #ifdef CONFIG_RCU_BOOST
         /* Unboost self if was boosted. */
-        if (special & RCU_READ_UNLOCK_BOOSTED) {
-                t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED;
-                rt_mutex_unlock(t->rcu_boost_mutex);
+        if (t->rcu_boost_mutex != NULL) {
+                rbmp = t->rcu_boost_mutex;
                 t->rcu_boost_mutex = NULL;
+                rt_mutex_unlock(rbmp);
         }
 #endif /* #ifdef CONFIG_RCU_BOOST */
         local_irq_restore(flags);
@@ -618,13 +638,22 @@ void __rcu_read_unlock(void)
         struct task_struct *t = current;
 
         barrier();  /* needed if we ever invoke rcu_read_unlock in rcutiny.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(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);
@@ -649,7 +678,7 @@ static void rcu_preempt_check_callbacks(void)
                 invoke_rcu_callbacks();
         if (rcu_preempt_gp_in_progress() &&
             rcu_cpu_blocking_cur_gp() &&
-            rcu_preempt_running_reader())
+            rcu_preempt_running_reader() > 0)
                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
 }
 
@@ -706,6 +735,11 @@ EXPORT_SYMBOL_GPL(call_rcu);
  */
 void synchronize_rcu(void)
 {
+        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
+                           !lock_is_held(&rcu_lock_map) &&
+                           !lock_is_held(&rcu_sched_lock_map),
+                           "Illegal synchronize_rcu() in RCU read-side critical section");
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
         if (!rcu_scheduler_active)
                 return;
@@ -882,7 +916,8 @@ static void rcu_preempt_process_callbacks(void)
 static void invoke_rcu_callbacks(void)
 {
         have_rcu_kthread_work = 1;
-        wake_up(&rcu_kthread_wq);
+        if (rcu_kthread_task != NULL)
+                wake_up(&rcu_kthread_wq);
 }
 
 #ifdef CONFIG_RCU_TRACE
@@ -943,12 +978,16 @@ early_initcall(rcu_spawn_kthreads);
 
 #else /* #ifdef CONFIG_RCU_BOOST */
 
+/* Hold off callback invocation until early_initcall() time. */
+static int rcu_scheduler_fully_active __read_mostly;
+
 /*
  * Start up softirq processing of callbacks.
  */
 void invoke_rcu_callbacks(void)
 {
-        raise_softirq(RCU_SOFTIRQ);
+        if (rcu_scheduler_fully_active)
+                raise_softirq(RCU_SOFTIRQ);
 }
 
 #ifdef CONFIG_RCU_TRACE
@@ -963,10 +1002,14 @@ static bool rcu_is_callbacks_kthread(void)
 
 #endif /* #ifdef CONFIG_RCU_TRACE */
 
-void rcu_init(void)
+static int __init rcu_scheduler_really_started(void)
 {
+        rcu_scheduler_fully_active = 1;
         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+        raise_softirq(RCU_SOFTIRQ);  /* Invoke any callbacks from early boot. */
+        return 0;
 }
+early_initcall(rcu_scheduler_really_started);
 
 #endif /* #else #ifdef CONFIG_RCU_BOOST */