On Tue, 5 Feb 2019 12:52:29 +0100 Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > On Mon, 4 Feb 2019 16:31:02 +0100 > Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > > > On Thu, 31 Jan 2019 13:34:55 +0100 > > Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > > > > > On Thu, 31 Jan 2019 12:52:20 +0100 > > > Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > > > > > > > On Wed, 30 Jan 2019 19:51:27 +0100 > > > > Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > > > > > > > > > On Wed, 30 Jan 2019 14:22:07 +0100 > > > > > Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > > > > > > > > > > > When we get a solicited interrupt, the start function may have > > > > > > been cleared by a csch, but we still have a channel program > > > > > > structure allocated. Make it safe to call the cp accessors in > > > > > > any case, so we can call them unconditionally. > > > > > > > > > > I read this like it is supposed to be safe regardless of > > > > > parallelism and threads. However I don't see any explicit > > > > > synchronization done for cp->initialized. > > > > > > > > > > I've managed to figure out how is that supposed to be safe > > > > > for the cp_free() (which is probably our main concern) in > > > > > vfio_ccw_sch_io_todo(), but if fail when it comes to the one > > > > > in vfio_ccw_mdev_notifier(). > > > > > > > > > > Can you explain us how does the synchronization work? > > > > > > > > You read that wrong, I don't add synchronization, I just add a check. > > > > > > > > > > Now I'm confused. Does that mean we don't need synchronization for this? > > > > If we lack synchronization (that is not provided by the current state > > machine handling, or the rework here), we should do a patch on top > > (preferably on top of the whole series, so this does not get even more > > tangled up.) This is really just about the extra check. > > > > I'm not a huge fan of keeping or introducing races -- it makes things > difficult to reason about, but I do have some understanging your > position. The only thing I want to avoid is knowingly making things worse than before, and I don't think this patch does that. > > This patch-series is AFAICT a big improvement over what we have. I would > like Farhan confirming that it makes these hick-ups when he used to hit > BUSY with another ssch request disappear. If it does (I hope it does) > it's definitely a good thing for anybody who wants to use vfio-ccw. Yep. There remains a lot to be done, but it's a first step. > > Yet I find it difficult to slap my r-b over racy code, or partial > solutions. In the latter case, when I lack conceptual clarity, I find it > difficult to tell if we are heading into the right direction, or is what > we build today going to turn against us tomorrow. Sorry for being a drag. As long as we don't introduce bad user space interfaces we have to drag around forever, I think anything is fair game if we think it's a good idea at that moment. We can rewrite things if it turned out to be a bad idea (although I'm not arguing for doing random crap, of course :)
