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

[Shanker Donthineni]

On 1/31/23 10:17, Shanker Donthineni wrote:
> 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)) {

Sorry typo "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