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Date: Tue, 22 Dec 2020 02:37:09 +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 1/4] sched/idle: Fix missing need_resched() check after rcu_idle_enter() Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP kthread (rcuog) to be serviced. Usually a wake up happening while running the idle task is spotted in one of the need_resched() checks carefully placed within the idle loop that can break to the scheduler. Unfortunately in default_idle_call(), the call to rcu_idle_enter() is already beyond the last need_resched() check and we may halt the CPU with a resched request unhandled, leaving the task hanging. Fix this with performing a last minute need_resched() check after calling rcu_idle_enter(). Reported-by: Paul E. McKenney <paulmck@...nel.org> Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf) Cc: stable@...r.kernel.org Cc: Peter Zijlstra <peterz@...radead.org> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Ingo Molnar<mingo@...nel.org> Signed-off-by: Frederic Weisbecker <frederic@...nel.org> --- kernel/sched/idle.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 305727ea0677..1af60dc50beb 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -109,15 +109,21 @@ void __cpuidle default_idle_call(void) rcu_idle_enter(); lockdep_hardirqs_on(_THIS_IP_); - arch_cpu_idle(); + /* + * Last need_resched() check must come after rcu_idle_enter() + * which may wake up RCU internal tasks. + */ + if (!need_resched()) { + arch_cpu_idle(); + raw_local_irq_disable(); + } /* - * OK, so IRQs are enabled here, but RCU needs them disabled to - * turn itself back on.. funny thing is that disabling IRQs - * will cause tracing, which needs RCU. Jump through hoops to - * make it 'work'. + * OK, so IRQs are enabled after arch_cpu_idle(), but RCU needs + * them disabled to turn itself back on.. funny thing is that + * disabling IRQs will cause tracing, which needs RCU. Jump through + * hoops to make it 'work'. */ - raw_local_irq_disable(); lockdep_hardirqs_off(_THIS_IP_); rcu_idle_exit(); lockdep_hardirqs_on(_THIS_IP_); -- 2.25.1
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