rcu: Suppress RCU lockdep warnings during early boot

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.

Also introduce a debug_lockdep_rcu_enabled() static inline
helper function, which tags the CONTINUE_PROVE_RCU case as
likely(), as suggested by Ingo Molnar.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1267631219-8713-2-git-send-email-paulmck@linux.vnet.ibm.com>
[ v2: removed incomplete debug_lockdep_rcu_update() bits ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index e22960ecb71ad6b290975d194ce7a66d71acc4f4..75921b83c0ab791b24bad0f7a74e3d831611b07e 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -97,6 +97,11 @@ extern struct lockdep_map rcu_sched_lock_map;
 # define rcu_read_release_sched() \
                lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
 
+static inline int debug_lockdep_rcu_enabled(void)
+{
+       return likely(rcu_scheduler_active && debug_locks);
+}
+
 /**
  * rcu_read_lock_held - might we be in RCU read-side critical section?
  *
@@ -104,12 +109,14 @@ 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 (!debug_lockdep_rcu_enabled())
+               return 1;
+       return lock_is_held(&rcu_lock_map);
 }
 
 /**
@@ -119,12 +126,14 @@ 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 (!debug_lockdep_rcu_enabled())
+               return 1;
+       return lock_is_held(&rcu_bh_lock_map);
 }
 
 /**
@@ -135,15 +144,19 @@ 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.
  */
 #ifdef CONFIG_PREEMPT
 static inline int rcu_read_lock_sched_held(void)
 {
        int lockdep_opinion = 0;
 
+       if (!debug_lockdep_rcu_enabled())
+               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_PREEMPT */
 static inline int rcu_read_lock_sched_held(void)
@@ -174,7 +187,7 @@ static inline int rcu_read_lock_bh_held(void)
 #ifdef CONFIG_PREEMPT
 static inline int rcu_read_lock_sched_held(void)
 {
-       return preempt_count() != 0 || !rcu_scheduler_active;
+       return !rcu_scheduler_active || preempt_count() != 0;
 }
 #else /* #ifdef CONFIG_PREEMPT */
 static inline int rcu_read_lock_sched_held(void)
@@ -198,7 +211,7 @@ static inline int rcu_read_lock_sched_held(void)
  */
 #define rcu_dereference_check(p, c) \
        ({ \
-               if (debug_locks && !(c)) \
+               if (debug_lockdep_rcu_enabled() && !(c)) \
                        lockdep_rcu_dereference(__FILE__, __LINE__); \
                rcu_dereference_raw(p); \
        })