If there is a flood of callbacks, it is necessary to put multiple CPUs to work invoking those callbacks. This commit therefore uses a workqueue-flooding approach to parallelize RCU Tasks callback execution. Reported-by: Martin Lau <kafai@fb.com> Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>