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

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Date:   Thu, 30 Nov 2017 12:20:46 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     xiaolong.ye@...el.com, frederic@...nel.org, tglx@...utronix.de,
        cmetcalf@...lanox.com, cl@...ux.com, torvalds@...ux-foundation.org,
        lcapitulino@...hat.com, efault@....de, peterz@...radead.org,
        riel@...hat.com, kernellwp@...il.com, mingo@...nel.org,
        john.stultz@...aro.org
Subject: [PATCH] sched/isolation: Make NO_HZ_FULL select CPU_ISOLATION

Commit 5c4991e24c69 ("sched/isolation: Split out new
CONFIG_CPU_ISOLATION=y config from CONFIG_NO_HZ_FULL") can result in RCU
CPU stall warnings when running rcutorture with CONFIG_NO_HZ_FULL_ALL=y
and CONFIG_CPU_ISOLATION=n.  These warnings are caused by RCU's
grace-period kthreads sleeping for a few jiffies, but never being
awakened:

[  116.353432] rcu_preempt kthread starved for 9974 jiffies! g4294967208
+c4294967207 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=0
[  116.355517] rcu_preempt     I 7464     8      2 0x80000000
[  116.356543] Call Trace:
[  116.357008]  __schedule+0x493/0x620
[  116.357682]  schedule+0x24/0x40
[  116.358291]  schedule_timeout+0x330/0x3b0
[  116.359024]  ? preempt_count_sub+0xea/0x140
[  116.359806]  ? collect_expired_timers+0xb0/0xb0
[  116.360660]  rcu_gp_kthread+0x6bf/0xef0

This commit therefore makes NO_HZ_FULL select CPU_ISOLATION, which
prevents this behavior and seems like it was the original intention in
any case.

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

Link: https://lkml.kernel.org/r/20171126084203.GE21779@yexl-desktop
Reported-by: kernel test robot <xiaolong.ye@...el.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Frederic Weisbecker <frederic@...nel.org>
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>

diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index e776fc8cc1df..f6b5f19223d6 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