Re: [Qemu-ppc] pseries on qemu-system-ppc64le crashes in doorbell_core_ipi()

[Frederic Weisbecker <frederic@kernel.org>]

On Mon, Apr 01, 2019 at 10:38:27AM +0200, Peter Zijlstra wrote:
> 
> + fweisbec, who did the remote bits
> 
> On Sat, Mar 30, 2019 at 01:10:28PM +1000, Nicholas Piggin wrote:
> > diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> > index 6b7cdf17ccf8..f0e539d0f879 100644
> > --- a/kernel/irq_work.c
> > +++ b/kernel/irq_work.c
> > -/* Enqueue the irq work @work on the current CPU */
> > -bool irq_work_queue(struct irq_work *work)
> > +/*
> > + * Enqueue the irq_work @work on @cpu unless it's already pending
> > + * somewhere.
> > + *
> > + * Can be re-enqueued while the callback is still in progress.
> > + */
> > +bool irq_work_queue_on(struct irq_work *work, int cpu)
> >  {
> > +#ifndef CONFIG_SMP
> > +	return irq_work_queue(work);
> > +

I'd suggest to use "if (!IS_ENABLED(CONFIG_SMP))" here to avoid the large
ifdeffery.

> > +#else /* #ifndef CONFIG_SMP */
> > +	/* All work should have been flushed before going offline */
> > +	WARN_ON_ONCE(cpu_is_offline(cpu));
> > +
> >  	/* Only queue if not already pending */
> >  	if (!irq_work_claim(work))
> >  		return false;
> >  
> > -	/* Queue the entry and raise the IPI if needed. */
> >  	preempt_disable();
> > -
> > -	/* If the work is "lazy", handle it from next tick if any */
> > -	if (work->flags & IRQ_WORK_LAZY) {
> > -		if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
> > -		    tick_nohz_tick_stopped())
> > -			arch_irq_work_raise();
> > -	} else {
> > -		if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
> > -			arch_irq_work_raise();
> > -	}
> > -
> > +	if (cpu != smp_processor_id()) {
> > +		/* Arch remote IPI send/receive backend aren't NMI safe */
> > +		WARN_ON_ONCE(in_nmi());
> > +		if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
> > +			arch_send_call_function_single_ipi(cpu);
> > +	} else
> > +		__irq_work_queue(work);

Also perhaps rename __irq_work_queue() to irq_work_queue_local() to make it
instantly clearer to reviewers.

Other than those cosmetic changes,

  Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

Thanks.