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Date: Tue, 22 Dec 2020 02:37:11 +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 3/4] ARM: imx6q: 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 imx6q_enter_wait() is beyond the last generic need_resched() check and it performs a wfi right away after the call to rcu_idle_enter(). 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: 1a67b9263e06 (ARM: imx6q: Fixup RCU usage for cpuidle) Cc: stable@...r.kernel.org Cc: Shawn Guo <shawnguo@...nel.org> Cc: Sascha Hauer <s.hauer@...gutronix.de> Cc: Pengutronix Kernel Team <kernel@...gutronix.de> Cc: Fabio Estevam <festevam@...il.com> Cc: NXP Linux Team <linux-imx@....com> 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> --- arch/arm/mach-imx/cpuidle-imx6q.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/arm/mach-imx/cpuidle-imx6q.c b/arch/arm/mach-imx/cpuidle-imx6q.c index 094337dc1bc7..31a60d257d3d 100644 --- a/arch/arm/mach-imx/cpuidle-imx6q.c +++ b/arch/arm/mach-imx/cpuidle-imx6q.c @@ -25,7 +25,12 @@ static int imx6q_enter_wait(struct cpuidle_device *dev, raw_spin_unlock(&cpuidle_lock); rcu_idle_enter(); - cpu_do_idle(); + /* + * Last need_resched() check must come after rcu_idle_enter() + * which may wake up RCU internal tasks. + */ + if (!need_resched()) + cpu_do_idle(); rcu_idle_exit(); raw_spin_lock(&cpuidle_lock); -- 2.25.1
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