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. Also, thinking about it some more, I think I like the non-wrapped pollcb variant better now. This is because I can uhook the wqh in the POLLHUP and defer the kref_put() until later. I think this combination gives me the most ideal environment (even though technically I should not expect more activity on the wait-queue after the POLLHUP). In either case, I whipped up a super-lite patch with just the bare minimum and then developed the KVM solution on top. Things look really good, now, and I am happy with the result. As an aside, it only has the following impact on the eventfd core: fs/eventfd.c | 43 ++++++++++++++++++++++++++++++++++++------- include/linux/eventfd.h | 7 +++++++ 2 files changed, 43 insertions(+), 7 deletions(-) Ill post the series, including the KVM portions, for review. Thanks Davide, -Greg
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