On 21.04.2023 13:00, Volodymyr Babchuk wrote: > > Hello Roger, > > Roger Pau Monné <[email protected]> writes: > >> On Mon, Apr 17, 2023 at 12:34:31PM +0200, Jan Beulich wrote: >>> On 17.04.2023 12:17, Roger Pau Monné wrote: >>>> On Fri, Apr 14, 2023 at 01:30:39AM +0000, Volodymyr Babchuk wrote: >>>>> Above I have proposed another view on this. I hope, it will work for >>>>> you. Just to reiterate, idea is to allow "harmless" refcounts to be left >>>>> after returning from pci_remove_device(). By "harmless" I mean that >>>>> owners of those refcounts will not try to access the physical PCI >>>>> device if pci_remove_device() is already finished. >>>> >>>> I'm not strictly a maintainer of this piece code, albeit I have an >>>> opinion. I will like to also hear Jans opinion, since he is the >>>> maintainer. >>> >>> I'm afraid I can't really appreciate the term "harmless refcounts". Whoever >>> holds a ref is entitled to access the device. As stated before, I see only >>> two ways of getting things consistent: Either pci_remove_device() is >>> invoked upon dropping of the last ref, >> >> With this approach, what would be the implementation of >> PHYSDEVOP_manage_pci_remove? Would it just check whether the pdev >> exist and either return 0 or -EBUSY? >> > > Okay, I am preparing patches with the behavior you proposed. To test it, > I artificially set refcount to 2 and indeed PHYSDEVOP_manage_pci_remove > returned -EBUSY, which propagated to the linux driver. Problem is that > Linux driver can't do anything with this. It just displayed an error > message and removed device anyways. This is because Linux sends > PHYSDEVOP_manage_pci_remove in device_remove() call path and there is no > way to prevent the device removal. So, admin is not capable to try this > again.
So maybe Linux'es issuing of the call needs moving elsewhere? Or we need a new sub-op, such that PHYSDEVOP_manage_pci_remove can remain purely a last-moment notification? > As I workaround, I can create hypercall continuation in case if > pci_remove_device() returns -EBUSY. What is your opinion? How would that help? You'd then spin perhaps for hours or days ... Jan
