On Sat, Jul 18, 2020 at 11:47:52AM +0800, Wei Hu wrote:
> Kdump could fail sometime on Hyper-V guest over Accelerated Network
> interface. This is because the retry in hv_pci_enter_d0() relies on
> an asynchronous host event arriving before the guest calls
> hv_send_resources_allocated(). Fix the problem by moving retry
> to hv_pci_probe(), removing this dependency and making the calling
> sequence synchronous.
You have to explain why this code move fixes the problem and you
also have to add a comment to the code so that anyone who has to
fix it in the future can understand why the code is where you
are moving it to and why that's a solution.
> Fixes: c81992e7f4aa ("PCI: hv: Retry PCI bus D0 entry on invalid device state")
> Signed-off-by: Wei Hu <weh@xxxxxxxxxxxxx>
Please carry tags and send patches -in-reply-to the previous version
to allow threading.
Thanks,
Lorenzo
> ---
> v2: Adding Fixes tag according to Michael Kelley's review comment.
> v3: Fix couple typos and reword commit message to make it clearer.
> Thanks the comments from Bjorn Helgaas.
>
> drivers/pci/controller/pci-hyperv.c | 66 ++++++++++++++---------------
> 1 file changed, 32 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index bf40ff09c99d..738ee30f3334 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -2759,10 +2759,8 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
> struct pci_bus_d0_entry *d0_entry;
> struct hv_pci_compl comp_pkt;
> struct pci_packet *pkt;
> - bool retry = true;
> int ret;
>
> -enter_d0_retry:
> /*
> * Tell the host that the bus is ready to use, and moved into the
> * powered-on state. This includes telling the host which region
> @@ -2789,38 +2787,6 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
> if (ret)
> goto exit;
>
> - /*
> - * In certain case (Kdump) the pci device of interest was
> - * not cleanly shut down and resource is still held on host
> - * side, the host could return invalid device status.
> - * We need to explicitly request host to release the resource
> - * and try to enter D0 again.
> - */
> - if (comp_pkt.completion_status < 0 && retry) {
> - retry = false;
> -
> - dev_err(&hdev->device, "Retrying D0 Entry\n");
> -
> - /*
> - * Hv_pci_bus_exit() calls hv_send_resource_released()
> - * to free up resources of its child devices.
> - * In the kdump kernel we need to set the
> - * wslot_res_allocated to 255 so it scans all child
> - * devices to release resources allocated in the
> - * normal kernel before panic happened.
> - */
> - hbus->wslot_res_allocated = 255;
> -
> - ret = hv_pci_bus_exit(hdev, true);
> -
> - if (ret == 0) {
> - kfree(pkt);
> - goto enter_d0_retry;
> - }
> - dev_err(&hdev->device,
> - "Retrying D0 failed with ret %d\n", ret);
> - }
> -
> if (comp_pkt.completion_status < 0) {
> dev_err(&hdev->device,
> "PCI Pass-through VSP failed D0 Entry with status %x\n",
> @@ -3058,6 +3024,7 @@ static int hv_pci_probe(struct hv_device *hdev,
> struct hv_pcibus_device *hbus;
> u16 dom_req, dom;
> char *name;
> + bool enter_d0_retry = true;
> int ret;
>
> /*
> @@ -3178,11 +3145,42 @@ static int hv_pci_probe(struct hv_device *hdev,
> if (ret)
> goto free_fwnode;
>
> +retry:
> ret = hv_pci_query_relations(hdev);
> if (ret)
> goto free_irq_domain;
>
> ret = hv_pci_enter_d0(hdev);
> + /*
> + * In certain case (Kdump) the pci device of interest was
> + * not cleanly shut down and resource is still held on host
> + * side, the host could return invalid device status.
> + * We need to explicitly request host to release the resource
> + * and try to enter D0 again.
> + * The retry should start from hv_pci_query_relations() call.
> + */
> + if (ret == -EPROTO && enter_d0_retry) {
> + enter_d0_retry = false;
> +
> + dev_err(&hdev->device, "Retrying D0 Entry\n");
> +
> + /*
> + * Hv_pci_bus_exit() calls hv_send_resources_released()
> + * to free up resources of its child devices.
> + * In the kdump kernel we need to set the
> + * wslot_res_allocated to 255 so it scans all child
> + * devices to release resources allocated in the
> + * normal kernel before panic happened.
> + */
> + hbus->wslot_res_allocated = 255;
> + ret = hv_pci_bus_exit(hdev, true);
> +
> + if (ret == 0)
> + goto retry;
> +
> + dev_err(&hdev->device,
> + "Retrying D0 failed with ret %d\n", ret);
> + }
> if (ret)
> goto free_irq_domain;
>
> --
> 2.20.1
>
