[PATCH] sched/isolation: Make NO_HZ_FULL select CPU_ISOLATION

[Paul E. McKenney]

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: 20171126084203.GE21779@yexl-desktop">https://lkml.kernel.org/r/20171126084203.GE21779@yexl-desktop
Reported-by: kernel test robot <xiaolong.ye@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Wanpeng Li <kernellwp@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>

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