rcu: Mark accesses to boost_starttime

The boost_starttime shared variable has conflicting unmarked C-language
accesses, which are dangerous at best.  This commit therefore adds
appropriate marking.  This was found by KCSAN.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-12-13 11:05:07 -08:00
commit a47f9f131d