> From: Jason Wang <jasowang@xxxxxxxxxx> > Sent: Tuesday, January 11, 2022 10:17 AM > > > > I guess in this situation it would be better defer to the future patch > > to add such locking or wrapper, although right now there are just two > > additional calls taking the lock needlessly when vhost_vdpa_get_status > > is called. Maybe it's just me but I'm worried some future patch may > > calls the locked API wrapper thousands of times unintendedly, then the > > overhead becomes quite obvious. > > I'm fine to remove this if others agree on this. > > > > > > > > > > > >> Ok, but IMHO it might be better to get some comment here, otherwise > > >> it's quite confusing why the lock needs to be held. vhost_vdpa had > > >> done its own serialization in vhost_vdpa_unlocked_ioctl() through > > >> vhost_dev`mutex. > > > > > > > > > Right, but they are done for different levels, one is for vhost_dev > > > antoher is for vdpa_dev. > > The cf_mutex is introduced to serialize the command line configure > > thread (via netlink) and the upstream driver calls from either the > > vhost_dev or virtio_dev. I don't see a case, even in future, where the > > netlink thread needs to update the virtio status on the fly. Can you > > enlighten me why that is at all possible? > Sorry for my late response. Netlink reads the whole space while it is not getting modified by vhost/virtio driver side. A better to convert cf_mutex to rw_sem that clarifies the code more and still ensure that netlink doesn't read bytes while it is getting modified. Given that config bytes can be updated anytime and not on each field boundary, it is anyway not atomic. It was added where we wanted to modify the fields post creation, but eventually drop that idea. So yes, cf_mutex removal is fine too. > After some thought I don't see a case. I can think of NEEDS_RESET but it should > come with a config interrupt so we're probably fine without the mutex here. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
