From 43f24fc4acb673ec5e4140632a4f73869c4631a2 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 8 Feb 2022 17:16:35 +0100 Subject: [PATCH 6/9] lib/irq_poll: Declare IRQ_POLL softirq vector as ksoftirqd-parking safe The following warning may appear while setting a CPU down: NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!! The IRQ_POLL_SOFTIRQ vector can be raised during the hotplug cpu_down() path after ksoftirqd is parked and before the CPU actually dies. However this is handled afterward at the CPUHP_IRQ_POLL_DEAD stage where the queue gets migrated. Hence this warning can be considered spurious and the vector can join the "hotplug-safe" list. Reported-and-tested-by: Paul Menzel Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Paul E. McKenney Cc: Paul Menzel --- include/linux/interrupt.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index 9613326d2f8a..f40754caaefa 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -580,12 +580,15 @@ enum }; /* - * Ignoring the RCU vector after ksoftirqd is parked is fine - * because: - * 1) rcutree_migrate_callbacks() takes care of the queue. + * The following vectors can be safely ignored after ksoftirqd is parked: + * + * _ RCU: + * 1) rcutree_migrate_callbacks() migrates the queue. * 2) rcu_report_dead() reports the final quiescent states. + * + * _ IRQ_POLL: irq_poll_cpu_dead() migrates the queue */ -#define SOFTIRQ_HOTPLUG_SAFE_MASK (BIT(RCU_SOFTIRQ)) +#define SOFTIRQ_HOTPLUG_SAFE_MASK (BIT(RCU_SOFTIRQ) | BIT(IRQ_POLL_SOFTIRQ)) /* map softirq index to softirq name. update 'softirq_to_name' in * kernel/softirq.c when adding a new softirq. -- 2.36.0