rcu: Add tracing for _rcu_barrier()

This commit adds event tracing for _rcu_barrier() execution.  This
is defined only if RCU_TRACE=y.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2 files changed