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Message-Id: <20210104152058.36642-4-frederic@kernel.org>
Date: Mon, 4 Jan 2021 16:20:57 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Frederic Weisbecker <frederic@...nel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
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>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
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: 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 | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/arm/mach-imx/cpuidle-imx6q.c b/arch/arm/mach-imx/cpuidle-imx6q.c
index 094337dc1bc7..1115f4dc6d1d 100644
--- a/arch/arm/mach-imx/cpuidle-imx6q.c
+++ b/arch/arm/mach-imx/cpuidle-imx6q.c
@@ -5,6 +5,7 @@
#include <linux/cpuidle.h>
#include <linux/module.h>
+#include <linux/thread_info.h>
#include <asm/cpuidle.h>
#include <soc/imx/cpuidle.h>
@@ -25,7 +26,12 @@ 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 (!tif_need_resched())
+ cpu_do_idle();
rcu_idle_exit();
raw_spin_lock(&cpuidle_lock);
--
2.25.1
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