5 files changed, 61 insertions, 4 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index f409529ff35a..146d37d31778 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -226,6 +226,15 @@ static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
 }
 #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 
+#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
+bool rcu_lockdep_current_cpu_online(void);
+#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
+static inline bool rcu_lockdep_current_cpu_online(void)
+{
+        return 1;
+}
+#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 #ifdef CONFIG_PROVE_RCU
@@ -270,6 +279,9 @@ extern int debug_lockdep_rcu_enabled(void);
  * occur in the same context, for example, it is illegal to invoke
  * rcu_read_unlock() in process context if the matching rcu_read_lock()
  * was invoked from within an irq handler.
+ *
+ * Note that rcu_read_lock() is disallowed if the CPU is either idle or
+ * offline from an RCU perspective, so check for those as well.
  */
 static inline int rcu_read_lock_held(void)
 {
@@ -277,6 +289,8 @@ static inline int rcu_read_lock_held(void)
                 return 1;
         if (rcu_is_cpu_idle())
                 return 0;
+        if (!rcu_lockdep_current_cpu_online())
+                return 0;
         return lock_is_held(&rcu_lock_map);
 }
 
@@ -313,6 +327,9 @@ extern int rcu_read_lock_bh_held(void);
  * notice an extended quiescent state to other CPUs that started a grace
  * period. Otherwise we would delay any grace period as long as we run in
  * the idle task.
+ *
+ * Similarly, we avoid claiming an SRCU read lock held if the current
+ * CPU is offline.
  */
 #ifdef CONFIG_PREEMPT_COUNT
 static inline int rcu_read_lock_sched_held(void)
@@ -323,6 +340,8 @@ static inline int rcu_read_lock_sched_held(void)
                 return 1;
         if (rcu_is_cpu_idle())
                 return 0;
+        if (!rcu_lockdep_current_cpu_online())
+                return 0;
         if (debug_locks)
                 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
         return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index e1b005918bbb..9a323728e60c 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -99,15 +99,18 @@ long srcu_batches_completed(struct srcu_struct *sp);
  * power mode. This way we can notice an extended quiescent state to
  * other CPUs that started a grace period. Otherwise we would delay any
  * grace period as long as we run in the idle task.
+ *
+ * Similarly, we avoid claiming an SRCU read lock held if the current
+ * CPU is offline.
  */
 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 {
-        if (rcu_is_cpu_idle())
-                return 0;
-
         if (!debug_lockdep_rcu_enabled())
                 return 1;
-
+        if (rcu_is_cpu_idle())
+                return 0;
+        if (!rcu_lockdep_current_cpu_online())
+                return 0;
         return lock_is_held(&sp->dep_map);
 }
 
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 2bc4e135ff23..a86f1741cc27 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -88,6 +88,9 @@ EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
  * section.
  *
  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
+ *
+ * Note that rcu_read_lock() is disallowed if the CPU is either idle or
+ * offline from an RCU perspective, so check for those as well.
  */
 int rcu_read_lock_bh_held(void)
 {
@@ -95,6 +98,8 @@ int rcu_read_lock_bh_held(void)
                 return 1;
         if (rcu_is_cpu_idle())
                 return 0;
+        if (!rcu_lockdep_current_cpu_online())
+                return 0;
         return in_softirq() || irqs_disabled();
 }
 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index dccd2f78db4e..bcf7db2f2fd2 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -591,6 +591,35 @@ int rcu_is_cpu_idle(void)
 }
 EXPORT_SYMBOL(rcu_is_cpu_idle);
 
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Is the current CPU online?  Disable preemption to avoid false positives
+ * that could otherwise happen due to the current CPU number being sampled,
+ * this task being preempted, its old CPU being taken offline, resuming
+ * on some other CPU, then determining that its old CPU is now offline.
+ * It is OK to use RCU on an offline processor during initial boot, hence
+ * the check for rcu_scheduler_fully_active.
+ *
+ * Disable checking if in an NMI handler because we cannot safely report
+ * errors from NMI handlers anyway.
+ */
+bool rcu_lockdep_current_cpu_online(void)
+{
+        bool ret;
+
+        if (in_nmi())
+                return 1;
+        preempt_disable();
+        ret = cpu_online(smp_processor_id()) ||
+              !rcu_scheduler_fully_active;
+        preempt_enable();
+        return ret;
+}
+EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
 #endif /* #ifdef CONFIG_PROVE_RCU */
 
 /**
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index aa93b074bb2f..cecea84f4f3f 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1946,6 +1946,7 @@ void synchronize_sched_expedited(void)
         /* Note that atomic_inc_return() implies full memory barrier. */
         firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
         get_online_cpus();
+        WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
 
         /*
          * Each pass through the following loop attempts to force a