From bf29cb238dc0656e6564b6a94bb82e11d2129437 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 14 Dec 2017 19:18:25 +0100 Subject: [PATCH] sched/isolation: Make CONFIG_NO_HZ_FULL select CONFIG_CPU_ISOLATION 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. Reported-by: kernel test robot Signed-off-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Chris Metcalf Cc: Christoph Lameter Cc: John Stultz Cc: Linus Torvalds Cc: Luiz Capitulino Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Cc: Wanpeng Li Fixes: 5c4991e24c69 ("sched/isolation: Split out new CONFIG_CPU_ISOLATION=y config from CONFIG_NO_HZ_FULL") Link: http://lkml.kernel.org/r/1513275507-29200-2-git-send-email-frederic@kernel.org Signed-off-by: Ingo Molnar --- kernel/time/Kconfig | 1 + 1 file changed, 1 insertion(+) 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