Merge "locking/rwsem-xadd: Fix missed wakeup due to reordering of load"

	unsigned long flags;

	WAKE_Q(wake_q);

	/*

	* __rwsem_down_write_failed_common(sem)

	*   rwsem_optimistic_spin(sem)

	*     osq_unlock(sem->osq)

	*   ...

	*   atomic_long_add_return(&sem->count)

	*

	*      - VS -

	*

	*              __up_write()

	*                if (atomic_long_sub_return_release(&sem->count) < 0)

	*                  rwsem_wake(sem)

	*                    osq_is_locked(&sem->osq)

	*

	* And __up_write() must observe !osq_is_locked() when it observes the

	* atomic_long_add_return() in order to not miss a wakeup.

	*

	* This boils down to:

	*

	* [S.rel] X = 1                [RmW] r0 = (Y += 0)

	*         MB                         RMB

	* [RmW]   Y += 1               [L]   r1 = X

	*

	* exists (r0=1 /\ r1=0)

	*/

	smp_rmb();

	/*

	 * If a spinner is present, it is not necessary to do the wakeup.

	 * Try to do wakeup only if the trylock succeeds to minimize