srcu: Check for concurrent updates of heuristics

srcu: Check for concurrent updates of heuristics

SRCU maintains the ->srcu_n_exp_nodelay and ->reschedule_count values
to guide heuristics governing auto-expediting of normal SRCU grace
periods and grace-period-state-machine delays.  This commit adds KCSAN
ASSERT_EXCLUSIVE_WRITER() calls to check for concurrent updates to
these fields.

Signed-off-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>