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 <[email protected]> Fixes: 1a67b9263e06 (ARM: imx6q: Fixup RCU usage for cpuidle) Cc: [email protected] Cc: Shawn Guo <[email protected]> Cc: Sascha Hauer <[email protected]> Cc: Pengutronix Kernel Team <[email protected]> Cc: Fabio Estevam <[email protected]> Cc: NXP Linux Team <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Rafael J. Wysocki <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Signed-off-by: Frederic Weisbecker <[email protected]> --- 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
