linux-kernel - [PATCH tip/core/rcu 17/88] checkpatch: Remove checks for expedited grace periods

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Message-Id: <1495749601-21574-17-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Thu, 25 May 2017 14:58:50 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 17/88] 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 <paulmck@...ux.vnet.ibm.com>
---
 scripts/checkpatch.pl | 17 -----------------
 1 file changed, 17 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 4b9569fa931b..c7e4d73fe1ce 100755
--- a/scripts/checkpatch.pl
+++ b/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@...lude/asm-@) {
 			CHK("ARCH_DEFINES",
-- 
2.5.2