Re: [UNTESTED] KVM: do not call kvm_set_irq from irq disabled section

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Apr 21, 2010 at 08:58:48PM +0300, Gleb Natapov wrote:
> On Wed, Apr 21, 2010 at 02:37:34PM -0300, Marcelo Tosatti wrote:
> > On Wed, Apr 21, 2010 at 08:12:27PM +0300, Gleb Natapov wrote:
> > > On Wed, Apr 21, 2010 at 12:58:41PM -0300, Marcelo Tosatti wrote:
> > > > > Or could we make kvm_set_irq() atomic? Though the code path is a little long 
> > > > > for spinlock.
> > > > 
> > > > Yes, given the sleep-inside-RCU-protected section bug from
> > > > kvm_notify_acked_irq, either that or convert IRQ locking to SRCU.
> > > > 
> > > > But as you said, the code paths are long and potentially slow, so
> > > > probably SRCU is a better alternative.
> > > > 
> > > > Gleb?
> > > kvm_set_irq() was converted to rcu from mutex to make msix interrupt
> > > injection scalable.
> > 
> > We meant ioapic lock. See the last report from Ralf on this thread. 
> Can we solve the problem by calling ack notifier outside rcu read
> section in kvm_notify_acked_irq()?

The unregister path does

- remove_from_list(entry)
- synchronize_rcu
- kfree(entry)

So if kvm_notify_acked_irq sleeps, synchronize_rcu can succeed, and the
notifier entry can be freed.