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

index bf40ff09c99d..d1758986fbc9 100644

drivers/pci/controller/pci-hyperv.c +37 -34

@@ -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;
 

Signature · 1 line

2.20.1

-----Original Message-----
From: Lorenzo Pieralisi <[email protected]>
Sent: Monday, July 27, 2020 7:19 PM
To: Wei Hu <[email protected]>
Cc: KY Srinivasan <[email protected]>; Haiyang Zhang <[email protected]>; Stephen Hemminger <[email protected]>; [email protected]; [email protected]; [email protected]; linux- [email protected]; [email protected]; linux- [email protected]; Dexuan Cui <[email protected]>; Michael Kelley <[email protected]>
Subject: Re: [PATCH v4] PCI: hv: Fix a timing issue which causes kdump to fail occasionally

Quoted 31 lines · Wei Hu

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 <[email protected]>

Reviewed-by Michael Kelley <[email protected]>

---
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(-)

drivers/pci/controller/pci-hyperv.c

Quoted 2 lines

drivers/pci/controller/pci-hyperv.c +0 -0

I edited commit log and a comment in the code to fix a typo and pushed out to pci/hv.

Thanks,
Lorenzo