2 files changed, 13 insertions, 5 deletions

diff --git a/kernel/profile.c b/kernel/profile.c
index a6574a18514e..d6579d511069 100644
--- a/kernel/profile.c
+++ b/kernel/profile.c
@@ -331,7 +331,6 @@ out:
         local_irq_restore(flags);
         put_cpu();
 }
-EXPORT_SYMBOL_GPL(profile_hits);
 
 static int __devinit profile_cpu_callback(struct notifier_block *info,
                                         unsigned long action, void *__cpu)
@@ -401,6 +400,8 @@ void profile_hits(int type, void *__pc, unsigned int nr_hits)
 }
 #endif /* !CONFIG_SMP */
 
+EXPORT_SYMBOL_GPL(profile_hits);
+
 void profile_tick(int type)
 {
         struct pt_regs *regs = get_irq_regs();
diff --git a/kernel/sys.c b/kernel/sys.c
index c7675c1bfdf2..6e2101dec0fc 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -323,11 +323,18 @@ EXPORT_SYMBOL_GPL(blocking_notifier_chain_unregister);
 int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
                 unsigned long val, void *v)
 {
-        int ret;
+        int ret = NOTIFY_DONE;
 
-        down_read(&nh->rwsem);
-        ret = notifier_call_chain(&nh->head, val, v);
-        up_read(&nh->rwsem);
+        /*
+         * We check the head outside the lock, but if this access is
+         * racy then it does not matter what the result of the test
+         * is, we re-check the list after having taken the lock anyway:
+         */
+        if (rcu_dereference(nh->head)) {
+                down_read(&nh->rwsem);
+                ret = notifier_call_chain(&nh->head, val, v);
+                up_read(&nh->rwsem);
+        }
         return ret;
 }