When we hot-remove a device, usually the host sends us a PCI_EJECT message, and a PCI_BUS_RELATIONS message with bus_rel->device_count == 0. But when we do the quick hot-add/hot-remove test, the host may not send us the PCI_EJECT message, if the guest has not fully finished the initialization by sending the PCI_RESOURCES_ASSIGNED* message to the host, so it's potentially unsafe to only depend on the pci_destroy_slot() in hv_eject_device_work(), though create_root_hv_pci_bus() -> hv_pci_assign_slots() is not called in this case. Note: in this case, the host still sends the guest a PCI_BUS_RELATIONS message with bus_rel->device_count == 0.
And, in the quick hot-add/hot-remove test, we can have such a race: before pci_devices_present_work() -> new_pcichild_device() adds the new device into hbus->children, we may have already received the PCI_EJECT message, and hence the taklet handler hv_pci_onchannelcallback() may fail to find the "hpdev" by get_pcichild_wslot(hbus, dev_message->wslot.slot), so hv_pci_eject_device() is NOT called; later create_root_hv_pci_bus() -> hv_pci_assign_slots() creates the slot, and the PCI_BUS_RELATIONS message with bus_rel->device_count == 0 removes the device from hbus->children, and we end up being unable to remove the slot in hv_pci_remove() -> hv_pci_remove_slots().
The patch removes the slot in pci_devices_present_work() when the device is removed. This can address the above race. Note 1: pci_devices_present_work() and hv_eject_device_work() run in the singled-threaded hbus->wq, so there is not a double-remove issue for the slot. Note 2: we can't offload hv_pci_eject_device() from hv_pci_onchannelcallback() to the workqueue, because we need hv_pci_onchannelcallback() synchronously call hv_pci_eject_device() to poll the channel's ringbuffer to work around the "hangs in hv_compose_msi_msg()" issue: see commit de0aa7b2f97d ("PCI: hv: Fix 2 hang issues in hv_compose_msi_msg()")
Fixes: a15f2c08c708 ("PCI: hv: support reporting serial number as slot information") Signed-off-by: Dexuan Cui decui@microsoft.com Cc: stable@vger.kernel.org --- drivers/pci/controller/pci-hyperv.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index b489412e3502..82acd6155adf 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c @@ -1776,6 +1776,10 @@ static void pci_devices_present_work(struct work_struct *work) hpdev = list_first_entry(&removed, struct hv_pci_dev, list_entry); list_del(&hpdev->list_entry); + + if (hpdev->pci_slot) + pci_destroy_slot(hpdev->pci_slot); + put_pcichild(hpdev); }