linux-kernel - [PATCH 1/3] sched/isolation: Make NO_HZ_FULL select CPU

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Date:   Thu, 14 Dec 2017 15:14:51 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        John Stultz <john.stultz@...aro.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Christoph Lameter <cl@...ux.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>,
        kernel test robot <xiaolong.ye@...el.com>
Subject: [PATCH 1/3] sched/isolation: Make NO_HZ_FULL select CPU_ISOLATION

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

CONFIG_NO_HZ_FULL doesn't make sense without CONFIG_CPU_ISOLATION. In
fact enabling the first without the second is a regression as nohz_full=
boot parameter gets silently ignored.

Besides this unnatural combination hangs RCU gp kthread when running
rcutorture for reasons that are not yet fully understood:

	rcu_preempt kthread starved for 9974 jiffies! g4294967208
	+c4294967207 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=0
	rcu_preempt     I 7464     8      2 0x80000000
	Call Trace:
		__schedule+0x493/0x620
		schedule+0x24/0x40
		schedule_timeout+0x330/0x3b0
		? preempt_count_sub+0xea/0x140
		? collect_expired_timers+0xb0/0xb0
		rcu_gp_kthread+0x6bf/0xef0

This commit therefore makes NO_HZ_FULL select CPU_ISOLATION, which
prevents all these bad behaviours.

Fixes: 5c4991e24c69 ("sched/isolation: Split out new CONFIG_CPU_ISOLATION=y config from CONFIG_NO_HZ_FULL")

Reported-by: kernel test robot <xiaolong.ye@...el.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Wanpeng Li <kernellwp@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: John Stultz <john.stultz@...aro.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/time/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index e776fc8..f6b5f19 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -95,6 +95,7 @@ config NO_HZ_FULL
 	select RCU_NOCB_CPU
 	select VIRT_CPU_ACCOUNTING_GEN
 	select IRQ_WORK
+	select CPU_ISOLATION
 	help
 	 Adaptively try to shutdown the tick whenever possible, even when
 	 the CPU is running tasks. Typically this requires running a single
-- 
2.7.4