Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 3/4] ARM: imx6q: Fix missing need_resched() check after rcu_idle_enter() | Date | Mon, 4 Jan 2021 16:20:57 +0100 |
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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@kernel.org> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Fixes: 1a67b9263e06 (ARM: imx6q: Fixup RCU usage for cpuidle) Cc: stable@vger.kernel.org Cc: Shawn Guo <shawnguo@kernel.org> Cc: Sascha Hauer <s.hauer@pengutronix.de> Cc: Pengutronix Kernel Team <kernel@pengutronix.de> Cc: Fabio Estevam <festevam@gmail.com> Cc: NXP Linux Team <linux-imx@nxp.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.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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