Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull RCU updates from Paul E. McKenney:

 "The largest feature of this series is shrinking and simplification,
  with the following diffstat summary:

     79 files changed, 1496 insertions(+), 4211 deletions(-)

  In other words, this series represents a net reduction of more than 2700
  lines of code."

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 59248dcc6ef3..d9510e8522d4 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -369,6 +369,26 @@ static __always_inline int spin_trylock_irq(spinlock_t *lock)
 	raw_spin_trylock_irqsave(spinlock_check(lock), flags); \
 })
 
+/**
+ * spin_unlock_wait - Interpose between successive critical sections
+ * @lock: the spinlock whose critical sections are to be interposed.
+ *
+ * Semantically this is equivalent to a spin_lock() immediately
+ * followed by a spin_unlock().  However, most architectures have
+ * more efficient implementations in which the spin_unlock_wait()
+ * cannot block concurrent lock acquisition, and in some cases
+ * where spin_unlock_wait() does not write to the lock variable.
+ * Nevertheless, spin_unlock_wait() can have high overhead, so if
+ * you feel the need to use it, please check to see if there is
+ * a better way to get your job done.
+ *
+ * The ordering guarantees provided by spin_unlock_wait() are:
+ *
+ * 1.  All accesses preceding the spin_unlock_wait() happen before
+ *     any accesses in later critical sections for this same lock.
+ * 2.  All accesses following the spin_unlock_wait() happen after
+ *     any accesses in earlier critical sections for this same lock.
+ */
 static __always_inline void spin_unlock_wait(spinlock_t *lock)
 {
 	raw_spin_unlock_wait(&lock->rlock);