Virtualization - May 2022 - [PATCH V4 0/9] rework on the IRQ hardening of virtio

On Wed, 11 May 2022 10:22:59 +0800
Jason Wang <jasowang at redhat.com> wrote:
> >        CPU0
> >        ----
> >   lock(&vcdev->irq_lock);
> >   <Interrupt>
> >     lock(&vcdev->irq_lock);
> >
> >  *** DEADLOCK ***  
> 
> It looks to me we need to use write_lock_irq()/write_unlock_irq() to
> do the synchronization.
> 
> And we probably need to keep the
> read_lock_irqsave()/read_lock_irqrestore() logic since I can see the
> virtio_ccw_int_handler() to be called from process context (e.g from
> the io_subchannel_quiesce()).
> 
Sounds correct.

Regards,
Halil

On Wed, May 11, 2022 at 10:02 PM Halil Pasic <pasic at linux.ibm.com>
wrote:
>
> On Wed, 11 May 2022 10:22:59 +0800
> Jason Wang <jasowang at redhat.com> wrote:
>
> > >        CPU0
> > >        ----
> > >   lock(&vcdev->irq_lock);
> > >   <Interrupt>
> > >     lock(&vcdev->irq_lock);
> > >
> > >  *** DEADLOCK ***
> >
> > It looks to me we need to use write_lock_irq()/write_unlock_irq() to
> > do the synchronization.
> >
> > And we probably need to keep the
> > read_lock_irqsave()/read_lock_irqrestore() logic since I can see the
> > virtio_ccw_int_handler() to be called from process context (e.g from
> > the io_subchannel_quiesce()).
> >
>
> Sounds correct.
As Cornelia and Vineeth pointed out, all the paths the vring_interrupt
is called with irq disabled.

So I will use spin_lock()/spin_unlock() in the next version.

Thanks
>
> Regards,
> Halil
>