checkpatch: Remove checks for expedited grace periods

There was a time when the expedited grace-period primitives
(synchronize_rcu_expedited(), synchronize_rcu_bh_expedited(), and
synchronize_sched_expedited()) used rather antisocial kernel
facilities like try_stop_cpus().  However, they have since been
housebroken to use only single-CPU IPIs, and typically cause less
disturbance than a scheduling-clock interrupt.  Furthermore, this
disturbance can be eliminated entirely using NO_HZ_FULL on the
one hand or the rcupdate.rcu_normal boot parameter on the other.

This commit therefore removes checkpatch's complaints about use
of the expedited RCU primitives.

Signed-off-by: Paul E. McKenney <[email protected]>

scripts/checkpatch.pl

@@ -5533,23 +5533,6 @@ sub process {
 			}
 		}
 
-# Check for expedited grace periods that interrupt non-idle non-nohz
-# online CPUs.  These expedited can therefore degrade real-time response
-# if used carelessly, and should be avoided where not absolutely
-# needed.  It is always OK to use synchronize_rcu_expedited() and
-# synchronize_sched_expedited() at boot time (before real-time applications
-# start) and in error situations where real-time response is compromised in
-# any case.  Note that synchronize_srcu_expedited() does -not- interrupt
-# other CPUs, so don't warn on uses of synchronize_srcu_expedited().
-# Of course, nothing comes for free, and srcu_read_lock() and
-# srcu_read_unlock() do contain full memory barriers in payment for
-# synchronize_srcu_expedited() non-interruption properties.
-		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
-			WARN("EXPEDITED_RCU_GRACE_PERIOD",
-			     "expedited RCU grace periods should be avoided where they can degrade real-time response\n" . $herecurr);
-
-		}
-
 # check of hardware specific defines
 		if ($line =~ m@^.\s*\#\s*if.*\b(__i386__|__powerpc64__|__sun__|__s390x__)\b@ && $realfile !~ m@include/asm-@) {
 			CHK("ARCH_DEFINES",