Merge tag 'urgent-rcu.2023.06.11a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU fix from Paul McKenney:
 "This fixes a spinlock-initialization regression in SRCU that causes
  the SRCU notifier to fail.

  The fix simply adds the initialization, but introduces a #ifdef
  because there is no spinlock to initialize for the Tiny SRCU used in
  !SMP builds.

  Yes, it would be nice to abstract this somehow in order to hide it in
  SRCU, but I still don't see a good way of doing this"

* tag 'urgent-rcu.2023.06.11a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu:
  notifier: Initialize new struct srcu_usage field

Author: torvalds

include/linux/notifier.h

@@ -106,12 +106,22 @@ extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
 #define RAW_NOTIFIER_INIT(name)	{				\
 		.head = NULL }
 
+#ifdef CONFIG_TREE_SRCU
 #define SRCU_NOTIFIER_INIT(name, pcpu)				\
 	{							\
 		.mutex = __MUTEX_INITIALIZER(name.mutex),	\
 		.head = NULL,					\
+		.srcuu = __SRCU_USAGE_INIT(name.srcuu),		\
 		.srcu = __SRCU_STRUCT_INIT(name.srcu, name.srcuu, pcpu), \
 	}
+#else
+#define SRCU_NOTIFIER_INIT(name, pcpu)				\
+	{							\
+		.mutex = __MUTEX_INITIALIZER(name.mutex),	\
+		.head = NULL,					\
+		.srcu = __SRCU_STRUCT_INIT(name.srcu, name.srcuu, pcpu), \
+	}
+#endif
 
 #define ATOMIC_NOTIFIER_HEAD(name)				\
 	struct atomic_notifier_head name =			\