On Tue, Jun 18, 2019 at 06:27:22AM -0700, Christoph Hellwig wrote: > On Tue, Jun 18, 2019 at 10:13:24AM -0300, Jason Gunthorpe wrote: > > > I don't even think we even need to bother with the POISON, normal list > > > debugging will already catch a double unregistration anyway. > > > > mirror->hmm isn't a list so list debugging won't help. > > > > My concern when I wrote this was that one of the in flight patches I > > can't see might be depending on this double-unregister-is-safe > > behavior, so I wanted them to crash reliably. > > > > It is a really overly conservative thing to do.. > > mirror->list is a list, and if we do a list_del on it during the > second unregistration it will trip up on the list poisoning. With the previous loose coupling of the mirror and the range some code might rance to try to create a range without a mirror, which will now reliably crash with the poison. It isn't so much the double unregister that worries me, but racing unregister with range functions. Jason
