On Tue, 23 Apr 2019 15:41:34 -0400 Farhan Ali <alifm@xxxxxxxxxxxxx> wrote: > On 04/23/2019 01:42 PM, Halil Pasic wrote: > > One thing I'm confused about is, that we don't seem to prevent > > new I/O being submitted. That is we could still loop indefinitely > > if we get new IO after the 'kill I/O on the subchannel' is done but > > before the msch() with the disable is issued. > > So the quiesce function will be called in the remove, release functions > and also in the mdev reset callback via an ioctl VFIO_DEVICE_RESET. > > Now the release function is invoked in cases when we hot unplug the > device or the guest is gone (or anything that will close the vfio mdev > file descriptor, I believe). In such scenarios it's really the userspace > which is asking to release the device. Similar for remove, where the > user has to explicitly write to the remove file for the mdev to invoke > it. Under normal conditions no sane userspace should be doing > release/remove while there are still on going I/Os :) > > Me and Conny had some discussion on this in v1 of this patch: > https://marc.info/?l=kvm&m=155437117823248&w=2 > > > > > The 'flush all I/O' parts in the commit message and in the code make > > this even more confusing. > > Maybe...if it's too confusing it could be fixed, but IMHO I don't think > it's a dealbreaker. If anyone else thinks otherwise, I can go ahead and > change it. I think it's fine -- I wasn't confused. > > > > > Another thing that I don't quite understand is injecting interrupts > > into QEMU for stuff that is actually not guest initiated. > > As mentioned above under normal conditions we shouldn't be doing > quiesce. But wouldn't those interrupts just be unsolicited interrupts > for the guest? Yes, you simply cannot keep an enabled subchannel from getting status pending with unsolicited status. > > > > > Furthermore I find how cio_cancel_halt_clear() quite confusing. We Well, that's a problem (if any) with the common I/O layer and beyond the scope of this patch. > > TL;DR: > > > > I welcome this batch (with an r-b) but I would like the commit message So, what does this sentence mean? Confused. > > and the comment changed so that the misleading 'flush all I/O in the > > workqueue'. > > > > I think 'vfio-ccw: fix cio_cancel_halt_clear() usage' would reflect the > > content of this patch better, because reasoning about the upper limit, > > and what happens if this upper limit is hit is not what this patch is > > about. It is about a client code bug that rendered iretry ineffective. > > > > I politely disagree with the change in subject line. I think the current > subject line describe what we are trying to prevent with this patch. But > again if anyone else feels otherwise, I will go ahead and change :) No, I agree that the subject line is completely fine.
