Re: [PATCH 3/5] iommu/s390: Use RCU to allow concurrent domain_list iteration

[Niklas Schnelle]

On Thu, 2022-10-20 at 08:05 -0300, Jason Gunthorpe wrote:
> On Thu, Oct 20, 2022 at 10:51:10AM +0200, Niklas Schnelle wrote:
> 
> > Ok that makes sense thanks for the explanation. So yes my assessment is
> > still that in this situation the IOTLB flush is architected to return
> > an error that we can ignore. Not the most elegant I admit but at least
> > it's simple. Alternatively I guess we could use call_rcu() to do the
> > zpci_unregister_ioat() but I'm not sure how to then make sure that a
> > subsequent zpci_register_ioat() only happens after that without adding
> > too much more logic.
> 
> This won't work either as the domain could have been freed before the
> call_rcu() happens, the domain needs to be detached synchronously
> 
> Jason

Yeah right, that is basically the same issue I was thinking of for a
subsequent zpci_register_ioat(). What about the obvious one. Just call
synchronize_rcu() before zpci_unregister_ioat()?