From 3ad81779ad35cd2e2ab34ba3f47f6f485696a105 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 2 Jul 2015 11:55:40 -0700 Subject: [PATCH] scripts: Make checkpatch.pl warn on expedited RCU grace periods The synchronize_rcu_expedited() and synchronize_sched_expedited() expedited-grace-period primitives induce OS jitter, which can degrade real-time response. This commit therefore adds a checkpatch.pl warning on any patch adding them. Note that this patch does not warn on synchronize_srcu_expedited() because it does not induce OS jitter, courtesy of its otherwise much-maligned read-side memory barriers. Signed-off-by: Paul E. McKenney Cc: Andy Whitcroft Cc: Joe Perches --- scripts/checkpatch.pl | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl index 90e1edc8dd42..976e7117edfb 100755 --- a/scripts/checkpatch.pl +++ b/scripts/checkpatch.pl @@ -5011,6 +5011,7 @@ sub process { "memory barrier without comment\n" . $herecurr); } } + # check for waitqueue_active without a comment. if ($line =~ /\bwaitqueue_active\s*\(/) { if (!ctx_has_comment($first_line, $linenr)) { @@ -5018,6 +5019,24 @@ sub process { "waitqueue_active without comment\n" . $herecurr); } } + +# Check for expedited grace periods that interrupt non-idle non-nohz +# online CPUs. These expedited can therefore degrade real-time response +# if used carelessly, and should be avoided where not absolutely +# needed. It is always OK to use synchronize_rcu_expedited() and +# synchronize_sched_expedited() at boot time (before real-time applications +# start) and in error situations where real-time response is compromised in +# any case. Note that synchronize_srcu_expedited() does -not- interrupt +# other CPUs, so don't warn on uses of synchronize_srcu_expedited(). +# Of course, nothing comes for free, and srcu_read_lock() and +# srcu_read_unlock() do contain full memory barriers in payment for +# synchronize_srcu_expedited() non-interruption properties. + if ($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", -- 2.30.2