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Date: Tue, 22 Dec 2020 02:37:08 +0100 From: Frederic Weisbecker <frederic@...nel.org> To: LKML <linux-kernel@...r.kernel.org> Cc: Frederic Weisbecker <frederic@...nel.org>, "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Fabio Estevam <festevam@...il.com>, stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, "Paul E . McKenney" <paulmck@...nel.org>, Len Brown <lenb@...nel.org>, Pengutronix Kernel Team <kernel@...gutronix.de>, NXP Linux Team <linux-imx@....com>, Daniel Lezcano <daniel.lezcano@...aro.org>, Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de> Subject: [PATCH 0/4] sched/idle: Fix missing need_resched() checks after rcu_idle_enter() With Paul, we've been thinking that the idle loop wasn't twisted enough yet to deserve 2020. rcutorture, after some recent parameter changes, has been complaining about a hung task. It appears that rcu_idle_enter() may wake up a NOCB kthread but this happens after the last generic need_resched() check. Some cpuidle drivers fix it by chance but many others don't. Here is a proposed bunch of fixes. I will need to also fix the rcu_user_enter() case, likely using irq_work, since nohz_full requires irq work to support self IPI. Also more generally, this raise the question of local task wake_up() under disabled interrupts. When a wake up occurs in a preempt disabled section, it gets handled by the outer preempt_enable() call. There is no similar mechanism when a wake up occurs with interrupts disabled. I guess it is assumed to be handled, at worst, in the next tick. But a local irq work would provide instant preemption once IRQs are re-enabled. Of course this would only make sense in CONFIG_PREEMPTION, and when the tick is disabled... git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git sched/idle HEAD: f2fa6e4a070c1535b9edc9ee097167fd2b15d235 Thanks, Frederic --- Frederic Weisbecker (4): sched/idle: Fix missing need_resched() check after rcu_idle_enter() cpuidle: Fix missing need_resched() check after rcu_idle_enter() ARM: imx6q: Fix missing need_resched() check after rcu_idle_enter() ACPI: processor: Fix missing need_resched() check after rcu_idle_enter() arch/arm/mach-imx/cpuidle-imx6q.c | 7 ++++++- drivers/acpi/processor_idle.c | 10 ++++++++-- drivers/cpuidle/cpuidle.c | 33 +++++++++++++++++++++++++-------- kernel/sched/idle.c | 18 ++++++++++++------ 4 files changed, 51 insertions(+), 17 deletions(-)
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