[PATCH RFC tip/core/rcu 1/2] rcu: suppress RCU lockdep warnings during early boot

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

RCU is used during very early boot, before RCU and lockdep have been
initialized.  So make the underlying primitives (rcu_read_lock_held(),
rcu_read_lock_bh_held(), rcu_read_lock_sched_held(), and
rcu_dereference_check()) check for early boot via the rcu_scheduler_active
flag.  This will suppress false positives.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h |   26 +++++++++++++++++---------
 1 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index c843736..af51d5f 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -104,12 +104,14 @@ extern struct lockdep_map rcu_sched_lock_map;
  * an RCU read-side critical section.  In absence of CONFIG_PROVE_LOCKING,
  * this assumes we are in an RCU read-side critical section unless it can
  * prove otherwise.
+ *
+ * Check rcu_scheduler_active to prevent false positives during boot.
  */
 static inline int rcu_read_lock_held(void)
 {
-	if (debug_locks)
-		return lock_is_held(&rcu_lock_map);
-	return 1;
+	if (!rcu_scheduler_active || !debug_locks)
+		return 1;
+	return lock_is_held(&rcu_lock_map);
 }
 
 /**
@@ -119,12 +121,14 @@ static inline int rcu_read_lock_held(void)
  * an RCU-bh read-side critical section.  In absence of CONFIG_PROVE_LOCKING,
  * this assumes we are in an RCU-bh read-side critical section unless it can
  * prove otherwise.
+ *
+ * Check rcu_scheduler_active to prevent false positives during boot.
  */
 static inline int rcu_read_lock_bh_held(void)
 {
-	if (debug_locks)
-		return lock_is_held(&rcu_bh_lock_map);
-	return 1;
+	if (!rcu_scheduler_active || !debug_locks)
+		return 1;
+	return lock_is_held(&rcu_bh_lock_map);
 }
 
 /**
@@ -135,14 +139,18 @@ static inline int rcu_read_lock_bh_held(void)
  * this assumes we are in an RCU-sched read-side critical section unless it
  * can prove otherwise.  Note that disabling of preemption (including
  * disabling irqs) counts as an RCU-sched read-side critical section.
+ *
+ * Check rcu_scheduler_active to prevent false positives during boot.
  */
 static inline int rcu_read_lock_sched_held(void)
 {
 	int lockdep_opinion = 0;
 
+	if (!rcu_scheduler_active || !debug_locks)
+		return 1;
 	if (debug_locks)
 		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
-	return lockdep_opinion || preempt_count() != 0 || !rcu_scheduler_active;
+	return lockdep_opinion || preempt_count() != 0;
 }
 
 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -166,7 +174,7 @@ static inline int rcu_read_lock_bh_held(void)
 
 static inline int rcu_read_lock_sched_held(void)
 {
-	return preempt_count() != 0 || !rcu_scheduler_active;
+	return !rcu_scheduler_active || preempt_count() != 0;
 }
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -184,7 +192,7 @@ static inline int rcu_read_lock_sched_held(void)
  */
 #define rcu_dereference_check(p, c) \
 	({ \
-		if (debug_locks && !(c)) \
+		if (rcu_scheduler_active && debug_locks && !(c)) \
 			lockdep_rcu_dereference(__FILE__, __LINE__); \
 		rcu_dereference_raw(p); \
 	})
-- 
1.6.6