Re: [PATCH 15/15] KVM: Fix racy in kvm_free_assigned_irq

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Dec 31, 2008 at 01:43:54PM +0800, Sheng Yang wrote:
> On Wednesday 31 December 2008 00:45:51 Marcelo Tosatti wrote:
> > On Tue, Dec 30, 2008 at 10:14:09AM +0800, Sheng Yang wrote:
> > > > There is one remaining issue: kvm_assigned_dev_interrupt_work_handler
> > > > can re-enable the interrupt for KVM_ASSIGNED_DEV_GUEST_MSI case.
> > > > Perhaps you need a new flag to indicate shutdown (so the host IRQ won't
> > > > be reenabled).
> > >
> > > Is it already covered by disable_irq_no_sync() before cancel_work_sync()?
> > > I've noted this in my comment: the irq may be disabled nested(once for
> > > MSI and twice for INTx), but I think it's fine for we're going to free
> > > it.
> >
> > The problem is that the irq can be re-enabled in
> > kvm_assigned_dev_interrupt_work_handler:
> >
> >
> > context 1               |    context 2
> >
> > disable_irq_nosync
> >                             kvm_assigned_dev_interrupt_work_handler
> >                             enable_irq
> > cancel_work_sync
> >
> > free_irq
> >
> 
> Um... My understanding is a little different...
> 
> Before context1 execute disable_irq_nosync(), in irq handler, 
> disable_irq_nosync() would also been executed. So only one enable_irq() is not 
> really enable irq here, which can cover the window at all. That's what I means 
> nested disable irq...

You're right. There have been two disable_irq calls.

OK, looks good to me.