The ->n_force_qs_lh field is accessed without the benefit of any
synchronization, so this commit adds the needed ACCESS_ONCE() wrappers.
Yes, increments to ->n_force_qs_lh can be lost, but contention should
be low and the field is strictly statistical in nature, so this is not
a problem.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>