irq_poll: Use raise_softirq_irqoff() in cpu_dead notifier

__raise_softirq_irqoff() adds a bit to the pending sofirq mask and this
is it. The softirq won't be handled in a deterministic way but randomly
when an interrupt fires and handles softirq in its irq_exit() routine or
if something randomly checks and handles pending softirqs in the call
chain before the CPU goes idle.

Add a local_bh_disable/enable() around the IRQ-off section which will
handle pending softirqs.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lkml.kernel.org/r/20210930103754.2128949-1-bigeasy@linutronix.de

lib/irq_poll.c

@@ -191,11 +191,13 @@ static int irq_poll_cpu_dead(unsigned int cpu)
 	 * If a CPU goes away, splice its entries to the current CPU
 	 * and trigger a run of the softirq
 	 */
+	local_bh_disable();
 	local_irq_disable();
 	list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
 			 this_cpu_ptr(&blk_cpu_iopoll));
 	__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
 	local_irq_enable();
+	local_bh_enable();
 
 	return 0;
 }