Re: [Xen-devel] [PATCH] dpci: Put the dpci back on the list if scheduled from another CPU.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Mar 17, 2015 at 04:06:14PM +0000, Jan Beulich wrote:
> >>> On 17.03.15 at 16:38, <konrad.wilk@xxxxxxxxxx> wrote:
> > --- a/xen/drivers/passthrough/io.c
> > +++ b/xen/drivers/passthrough/io.c
> > @@ -804,7 +804,17 @@ static void dpci_softirq(void)
> >          d = pirq_dpci->dom;
> >          smp_mb(); /* 'd' MUST be saved before we set/clear the bits. */
> >          if ( test_and_set_bit(STATE_RUN, &pirq_dpci->state) )
> > -            BUG();
> > +        {
> > +            unsigned long flags;
> > +
> > +            /* Put back on the list and retry. */
> > +            local_irq_save(flags);
> > +            list_add_tail(&pirq_dpci->softirq_list, &this_cpu(dpci_list));
> > +            local_irq_restore(flags);
> > +
> > +            raise_softirq(HVM_DPCI_SOFTIRQ);
> > +            continue;
> > +        }
> 
> As just said in another mail - unless there are convincing new
> arguments in favor of this (more of a hack than a real fix), I'm
> not going to accept it and instead consider reverting the
> offending commit. Iirc the latest we had come to looked quite a
> bit better than this one.

The latest one (please see attached) would cause an dead-lock iff
on the CPU we are running the softirq and an do_IRQ comes for the
exact dpci we are in process of executing.

> 
> Jan
>

Attachment: 0001-dpci-when-scheduling-spin-until-STATE_RUN-or-STATE_S.patch
Description: Text document

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