tree b1ccb9fd4b7a38ffcb6c93114059018b1ee7165d
parent 0cabb47af3cfaeb6007ba3868379bbd4daee64cc
author Paul E. McKenney <paulmck@kernel.org> 1639516518 -0800
committer Paul E. McKenney <paulmck@kernel.org> 1644343948 -0800

rcu: Rework rcu_barrier() and callback-migration logic

This commit reworks rcu_barrier() and callback-migration logic to
permit allowing rcu_barrier() to run concurrently with CPU-hotplug
operations.  The key trick is for callback migration to check to see if
an rcu_barrier() is in flight, and, if so, enqueue the ->barrier_head
callback on its behalf.

This commit adds synchronization with RCU's CPU-hotplug notifiers.  Taken
together, this will permit a later commit to remove the cpus_read_lock()
and cpus_read_unlock() calls from rcu_barrier().

[ paulmck: Updated per kbuild test robot feedback. ]
[ paulmck: Updated per reviews session with Neeraj, Frederic, Uladzislau, and Boqun. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>