On 09/07/2015 00:34, Jason Gunthorpe wrote: > On Wed, Jul 08, 2015 at 02:29:10PM -0600, Jason Gunthorpe wrote: >> On Mon, Jun 22, 2015 at 03:42:30PM +0300, Haggai Eran wrote: >>> An ib_client callback that is called with the lists_rwsem locked only for >>> read is protected from changes to the IB client lists, but not from >>> ib_unregister_device() freeing its client data. This is because >>> ib_unregister_device() will remove the device from the device list with >>> lists_rwsem locked for write, but perform the rest of the cleanup, >>> including the call to remove() without that lock. >> >> I was going to look at this, but, uh.. it seems mangled, doesn't >> apply, doesn't seem fixable from here. > > Okay, I see, it sits on top of the patch from Matan's last > posting.. My bad. No problem. > Hum... I have to say I don't really like this, changing the ordering > of client_data = NULL with respect to client->remove doesn't seem like > a great idea - and the rds changes look scary to me, at least I > couldn't confidently say they were OK.. > > And that isn't really the issue - this has nothing to do with > client_data, it is all about not having a callback running when doing > remove. > > It looks like the way out of this is to have ib_get_net_dev_by_params > iterate over the client_data_list and use a dedicated flag in that > struct to indicate that client&device combination is > remove-in-progress. > > This would be a bit more efficient as well, and I would suggest > passing the context in as an arg to the callback. > > client_data_list would change a bit to become write locked first by > write(lists_rwsem), and then second by the spin lock, so holding > read(lists_rwsem) while iterating is enough locking, and you'd hold > lists_rwsem while kfreeing. So, I don't want to keep lists_rwsem for write while calling add() and remove(). This would cause the deadlock that required the lists_rwsem patch in the first place. I guess I can drop lists_rwsem before the add/remove call and take it afterwards. Haggai -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
