> Subject: RE: [PATCH] PCI: hv: Fix a race condition when removing the device > > > From: Michael Kelley <mikelley@xxxxxxxxxxxxx> > > Sent: Wednesday, April 21, 2021 2:06 PM ... > > > Yes I think put_hvpcibus() and get_hvpcibus() can be removed, as we > > > have changed to use a dedicated workqueue for hbus since they were > > > introduced. > > > > > > But we still need to call tasklet_disable/enable() the same way > > > hv_pci_suspend() does, the > > > reason is that we need to protect hbus->state. This value needs to > > > be > > consistent for the > > > driver. For example, a CPU may decide to schedule a work on a work > > > queue > > that we just > > > flushed or destroyed, by reading the wrong hbus->state. > > > > > > > Yes, I would agree the tasklet disable/enable are needed, especially > > since > > tasklet_disable() > > is what ensures that the tasklet is not currently running. > > > > If the hbus ref counting isn't needed any longer, I would strongly > > recommend adding a patch to the series that removes it. This > > synchronization stuff is hard enough to understand and reason about; > > having a leftover mechanism that doesn't really do anything useful > > makes it nearly impossible. :-) > > > > Dexuan -- I'm hoping you can take a look as well and see if you agree. > > > > Michael > > I also think we can remove the reference counting. > > But it looks like there is still race in hv_pci_remove() even with Long's > patch: in hv_pci_remove(), we disable the tasklet, change hbus->state to > hv_pcibus_removing, re-enable the tasklet and flush hbus->wq, and set > hbus->state to hv_pcibus_removed -- what if the channel callback runs > again? -- now hbus->state is no longer hv_pcibus_removing, so > hv_pci_devices_present() -> hv_pci_start_relations_work() and > hv_pci_eject_device() can still add new work items to hbus->wq, and the > new work items may race with the vmbus_close(). Good catch, adding a check for hv_pcibus_removed should fix it. I'm sending a v2. > > It looks like we should remove the state hv_pcibus_removed? > > Thanks, > -- Dexuan
