Hi Daniel, On Monday, 4 September 2017 12:04:38 EEST Daniel Vetter wrote: > On Mon, Sep 04, 2017 at 11:41:05AM +0300, Laurent Pinchart wrote: > > On Monday, 4 September 2017 10:26:15 EEST Daniel Vetter wrote: [snip] > >> Yup, expect imo this should be done in drm core (as much as possible, > >> i.e. for ioctl at least, standard sysfs), plus then enter/exit exported > >> to drivers for their stuff. > >> > >> And it really needs to be srcu. For kms drivers the atomic_inc/dec wont > >> matter, for render drivers it will show up (some of our ioctls are 100% > >> lock less in the fastpath, not a single atomic op in there). > > > > Don't forget that we need to check the disconnect flag when entering > > ioctls to return -ENODEV. I'm open to clever solutions, but I'd first aim > > for correctness with a lock and then replace the internal implementation. > > As Noralf pointed out, we already check for drm_dev_is_unplugged(). Maybe > not in all places, but that can be fixed. Yes, but I believe that both the unplugged check and enter reference get need to be done atomically. > And you can't first make all ioctl slower and then fix it up, at least not > spread over multiple patch series. I guess for developing, doing the > simpler atomic counter first is ok. But the same patch series needs to > move over to srcu at the end. To SRCU or something similar, yes. > But I'm not sure that's a good idea, since implementing this 100% correctly > using your atomic_t idea means you implement half of srcu anyway. Otoh > discovering all those races should be an interesting journey :-) -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
