Date:   Mon, 27 Jul 2020 15:17:31 +0800
From:   Wei Hu <weh@...rosoft.com>
To:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, lorenzo.pieralisi@....com, robh@...nel.org,
        bhelgaas@...gle.com, linux-hyperv@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        decui@...rosoft.com, mikelley@...rosoft.com
Cc:     Wei Hu <weh@...rosoft.com>
Subject: [PATCH v4] PCI: hv: Fix a timing issue which causes kdump to fail occasionally

Kdump could fail sometime on Hyper-V guest over Accelerated Network
interface. This is because the retry in hv_pci_enter_d0() releases
child device strurctures in hv_pci_bus_exit(). Although there is
a second asynchronous device relations message sending from the host,
if this message arrives guest after hv_send_resource_allocated() is
called, the retry would fail.

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

This problem only happens on Accelerated Network or SRIOV devices as
only such devices currently are attached under vmbus PCI bridge.

Fixes: c81992e7f4aa ("PCI: hv: Retry PCI bus D0 entry on invalid device state")
Signed-off-by: Wei Hu <weh@...rosoft.com>
Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
---
    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.
    v4: Adding more  problem descritpions in the commit message
    and code upon request from Lorenze Pieralisi.

 drivers/pci/controller/pci-hyperv.c | 71 +++++++++++++++--------------
 1 file changed, 37 insertions(+), 34 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index bf40ff09c99d..d1758986fbc9 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 +3145,47 @@ 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;
 
-- 
2.20.1

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