PCI: hv: Fix a timing issue which causes kdump to fail occasionally

Kdump could fail sometime on Hyper-V guest because the retry in
hv_pci_enter_d0() releases child device structures in hv_pci_bus_exit().

Although there is a second asynchronous device relations message sending
from the host, if this message arrives to the guest after
hv_send_resource_allocated() is called, the retry would fail.

Fix the problem by moving retry to hv_pci_probe() and start the retry
from hv_pci_query_relations() call.  This will cause a device relations
message to arrive to the guest synchronously; the guest would then be
able to rebuild the child device structures before calling
hv_send_resource_allocated().

Link: https://lore.kernel.org/r/20200727071731.18516-1-weh@microsoft.com
Fixes: c81992e7f4aa ("PCI: hv: Retry PCI bus D0 entry on invalid device state")
Signed-off-by: Wei Hu <weh@microsoft.com>
[lorenzo.pieralisi@arm.com: fixed a comment and commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index bf40ff0..d0033ff 100644 (file)
--- 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 @@ enter_d0_retry:
        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 +3145,47 @@ 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.
+        * Since the hv_pci_bus_exit() call releases structures
+        * of all its child devices, we need to start the retry from
+        * hv_pci_query_relations() call, requesting host to send
+        * the synchronous child device relations message before this
+        * information is needed in hv_send_resources_allocated()
+        * call later.
+        */
+       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;