core-rcu-2020-06-01

 - RCU-tasks update, including addition of RCU Tasks Trace for
   BPF use and TASKS_RUDE_RCU
 - kfree_rcu() updates.
 - Remove scheduler locking restriction
 - RCU CPU stall warning updates.
 - Torture-test updates.
 - Miscellaneous fixes and other updates.

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