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 <paul...@kernel.org>
Fixes: 1a67b9263e06 (ARM: imx6q: Fixup RCU usage for cpuidle)
Cc: sta...@vger.kernel.org
Cc: Shawn Guo <shawn...@kernel.org>
Cc: Sascha Hauer <s.ha...@pengutronix.de>
Cc: Pengutronix Kernel Team <ker...@pengutronix.de>
Cc: Fabio Estevam <feste...@gmail.com>
Cc: NXP Linux Team <linux-...@nxp.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Frederic Weisbecker <frede...@kernel.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
