Re: [PATCH v2 1/3] genirq: Use hlist for managing resend handlers

[Shanker Donthineni]

On 4/10/23 05:05, Marc Zyngier wrote:
> External email: Use caution opening links or attachments
>
>
> On Sun, 09 Apr 2023 13:00:27 +0100,
> Shanker Donthineni <sdonthineni@xxxxxxxxxx> wrote:
> > > > @@ -30,18 +31,17 @@ 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;
> > > > -             local_irq_disable();
> > > > +
> > > > +     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);
> > > > -             local_irq_enable();
> > > > +             raw_spin_lock(&irq_resend_lock);
> > >
> > > What makes it safe to drop the local_irq_*able()?
> > >
> > > tasklet_action_common() explicitly enables interrupts when calling the
> > > callback, so unless there is some other interrupt disabling that I
> > > can't immediately spot, the handler may run in the wrong context.
> >
> > Unless I am overlooking something, interrupts are disabled within the while
> > loop unless desc->handle_irq() is enabling it. The existing code disables
> > and enables interrupts for each handler invocation, whereas the modified
> > code does it only once for all outstanding handlers.
>
> Ah, you use raw_spinlock_irq() outside of the loop. I somehow glanced
> over that, apologies for the noise. Unless we expect a really long
> list of interrupts to be resent, your current code should be OK.

Thanks, I'll post v3 patches to address the other review comments.