Commit f96272a9 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

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: default avatarPaul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Paul Menzel <pmenzel@molgen.mpg.de>
parent 0345691b

include/linux/interrupt.h

+7 −4
Original line number Diff line number Diff line
@@ -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.