On Mon, 22 Jun 2009, Gregory Haskins wrote: > Davide Libenzi wrote: > > On Sun, 21 Jun 2009, Gregory Haskins wrote: > > > > > >> This looks great, Davide. I am fairly certain I can now solve the races > >> and even implement Michael's DEASSIGN feature with this patch in place. > >> I will actually fire it up tomorrow when I am back in the office and > >> give it a spin, but I do not spy any more races via visual inspection. > >> > >> Kind Regards, > >> -Greg > >> > >> PS: I was wrong with my previous statement about requiring an embeddable > >> object (eventfd_notifier for me, eventfd_pollcb for you). I think you > >> can technically solve this issue minimally by merely locking the POLLHUP > >> and exposing the kref. However, I think that leads to an more awkward > >> interface (e.g. we already have eventfd_fget() plus we add a new one > >> like eventfd_refget(), which might confuse users), so I prefer what you > >> did here. Just thought I would throw that out there in case you would > >> prefer to change even fewer lines. > >> > > > > I actually ended up exposing the eventfd context anyway, since IMO is a > > better option instead of holding references to the eventfd file (that > > makes VFS people uneasy). > > > > I liked "version - 1" better ;) > > I think ultimately we still want to hold the fget() for > eventfd_signal(), as it is the producer side. Without it, we have no > way of knowing when the last producer goes away if they happen to be an > in-kernel user. No you don't. Holding a file* reference does not give you any assurance whatsoever that the last consumer did not go away. The f_count value will simply be 1 (just you). If a producer side want to take proper action when the last consumer leaves the building, it needs to register a pollcb hook and handle POLLHUP. Exposing the opaque eventfd context, and basing the eventfd operations on that one (instead of the live referenced file*) is a cleaner interface. Can you please base your IRQfd bits on top of that, so that we can give this IRQfd thread a closure? - Davide -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
