-----Original Message-----
From: Dexuan Cui <decui@microsoft.com>
Sent: Tuesday, March 28, 2023 2:33 PM
To: bhelgaas@google.com; davem@davemloft.net; edumazet@google.com;
Haiyang Zhang [off-list ref]; Jake Oshins
[off-list ref]; kuba@kernel.org; kw@linux.com; KY Srinivasan
[off-list ref]; leon@kernel.org; linux-pci@vger.kernel.org;
lpieralisi@kernel.org; Michael Kelley (LINUX) [off-list ref];
pabeni@redhat.com; robh@kernel.org; saeedm@nvidia.com;
wei.liu@kernel.org; Long Li [off-list ref]; boqun.feng@gmail.com;
Wei Hu [off-list ref]
Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; linux-
rdma@vger.kernel.org; netdev@vger.kernel.org
Subject: RE: [PATCH 4/6] Revert "PCI: hv: Fix a timing issue which causes
kdump to fail occasionally"

quoted

From: Dexuan Cui <decui@microsoft.com>
Sent: Monday, March 27, 2023 9:51 PM
To: bhelgaas@google.com; davem@davemloft.net; Dexuan Cui
[off-list ref]; edumazet@google.com; Haiyang Zhang
[off-list ref]; Jake Oshins [off-list ref];
kuba@kernel.org; kw@linux.com; KY Srinivasan [off-list ref];
leon@kernel.org; linux-pci@vger.kernel.org; lpieralisi@kernel.org;
Michael Kelley (LINUX) [off-list ref]; pabeni@redhat.com;
robh@kernel.org; saeedm@nvidia.com; wei.liu@kernel.org; Long Li
[off-list ref]; boqun.feng@gmail.com
Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org;
linux-rdma@vger.kernel.org; netdev@vger.kernel.org
Subject: [PATCH 4/6] Revert "PCI: hv: Fix a timing issue which causes
kdump to fail occasionally"

This reverts commit d6af2ed29c7c1c311b96dac989dcb991e90ee195.

The statement "the hv_pci_bus_exit() call releases structures of all
its child devices" in commit d6af2ed29c7c is not true: in the path
hv_pci_probe() -> hv_pci_enter_d0() -> hv_pci_bus_exit(hdev, true):
the parameter "keep_devs" is true, so hv_pci_bus_exit() does *not*
release the child "struct hv_pci_dev *hpdev" that is created earlier
in
pci_devices_present_work() -> new_pcichild_device().

The commit d6af2ed29c7c was originally made in July 2020 for RHEL 7.7,
where the old version of hv_pci_bus_exit() was used; when the commit
was rebased and merged into the upstream, people didn't notice that
it's not really necessary. The commit itself doesn't cause any issue,
but it makes hv_pci_probe() more complicated. Revert it to facilitate
some upcoming changes to hv_pci_probe().

Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 drivers/pci/controller/pci-hyperv.c | 71
++++++++++++++---------------
 1 file changed, 34 insertions(+), 37 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c

b/drivers/pci/controller/pci-hyperv.c
index 46df6d093d68..48feab095a14 100644

--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c

@@ -3225,8 +3225,10 @@ static int hv_pci_enter_d0(struct hv_device

*hdev)

quoted

 	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 @@
-3253,6 +3255,38 @@ 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", @@

quoted

-3493,7 +3527,6 @@ 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;

 	/*

@@ -3633,47 +3666,11 @@ 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;

--

2.25.1

Acked-by: Wei Hu <redacted>