Re: [PATCH 1/5] genirq: Use hlist for managing resend handlers

[Shanker Donthineni]

On 1/31/23 02:59, Thomas Gleixner wrote:
> On Sun, Jan 29 2023 at 18:57, Shanker Donthineni wrote:
> > +/* hlist_head to handle software resend of interrupts: */
> > +static HLIST_HEAD(irq_resend_list);
> > +static DEFINE_RAW_SPINLOCK(irq_resend_lock);
> >
> >   /*
> >    * Run software resends of IRQ's
> > @@ -30,18 +31,16 @@ static DECLARE_BITMAP(irqs_resend, IRQ_BITMAP_BITS);
> >   static void resend_irqs(struct tasklet_struct *unused)
> >   {
> >        struct irq_desc *desc;
> > -     int irq;
> > -
> > -     while (!bitmap_empty(irqs_resend, nr_irqs)) {
> > -             irq = find_first_bit(irqs_resend, nr_irqs);
> > -             clear_bit(irq, irqs_resend);
> > -             desc = irq_to_desc(irq);
> > -             if (!desc)
> > -                     continue;
> > +     struct hlist_node *n;
> > +
> > +     raw_spin_lock_irq(&irq_resend_lock);
> > +     hlist_for_each_entry_safe(desc, n, &irq_resend_list, resend_node) {
> > +             hlist_del_init(&desc->resend_node);
> >                local_irq_disable();
> >                desc->handle_irq(desc);
> >                local_irq_enable();
> >        }
> > +     raw_spin_unlock_irq(&irq_resend_lock);
> The lock ordering is broken here. irq_sw_resend() is invoked with
> desc->lock held and takes irq_resend_lock.
>
> Lockdep clearly would have told you...
>
>          raw_spin_lock_irq(&irq_resend_lock);
>          while (!hlist_empty(...)) {
>                  desc = hlist_entry(irq_resend_list.first, ...);
>                  hlist_del_init(&desc->resend_node);
>                  raw_spin_unlock(&...);
>                  desc->handle_irq();
>                  raw_spin_lock(&...);
>          }

Thanks for catching mistakes, I'll change it to this, please correct me if
I'm doing another mistake.

static void resend_irqs(struct tasklet_struct *unused)
{
        struct irq_desc *desc;

        raw_spin_lock_irq(&irq_resend_lock);
        while (hlist_empty(&irq_resend_list)) {
                desc = hlist_entry(irq_resend_list.first, struct irq_desc,
                                   resend_node);
                hlist_del_init(&desc->resend_node);
                raw_spin_unlock(&irq_resend_lock);
                desc->handle_irq(desc);
                raw_spin_lock(&irq_resend_lock);
        }
        raw_spin_unlock_irq(&irq_resend_lock);
}

Thanks,
Shanker