It was found that unloading 'hid_hyperv' module results in a devres
complaint:

 ...
 hv_vmbus: unregistering driver hid_hyperv
 ------------[ cut here ]------------
 WARNING: CPU: 2 PID: 3983 at drivers/base/devres.c:691 devres_release_group+0x1f2/0x2c0
 ...
 Call Trace:
  <TASK>
  ? devres_release_group+0x1f2/0x2c0
  ? __warn+0xd1/0x1c0
  ? devres_release_group+0x1f2/0x2c0
  ? report_bug+0x32a/0x3c0
  ? handle_bug+0x53/0xa0
  ? exc_invalid_op+0x18/0x50
  ? asm_exc_invalid_op+0x1a/0x20
  ? devres_release_group+0x1f2/0x2c0
  ? devres_release_group+0x90/0x2c0
  ? rcu_is_watching+0x15/0xb0
  ? __pfx_devres_release_group+0x10/0x10
  hid_device_remove+0xf5/0x220
  device_release_driver_internal+0x371/0x540
  ? klist_put+0xf3/0x170
  bus_remove_device+0x1f1/0x3f0
  device_del+0x33f/0x8c0
  ? __pfx_device_del+0x10/0x10
  ? cleanup_srcu_struct+0x337/0x500
  hid_destroy_device+0xc8/0x130
  mousevsc_remove+0xd2/0x1d0 [hid_hyperv]
  device_release_driver_internal+0x371/0x540
  driver_detach+0xc5/0x180
  bus_remove_driver+0x11e/0x2a0
  ? __mutex_unlock_slowpath+0x160/0x5e0
  vmbus_driver_unregister+0x62/0x2b0 [hv_vmbus]
  ...

And the issue seems to be that the corresponding devres group is not
allocated. Normally, devres_open_group() is called from
__hid_device_probe() but Hyper-V HID driver overrides 'hid_dev->driver'
with 'mousevsc_hid_driver' stub and basically re-implements
__hid_device_probe() by calling hid_parse() and hid_hw_start() but not
devres_open_group(). hid_device_probe() does not call __hid_device_probe()
for it. Later, when the driver is removed, hid_device_remove() calls
devres_release_group() as it doesn't check whether hdev->driver was
initially overridden or not.

The issue seems to be related to the commit 62c68e7cee33 ("HID: ensure
timely release of driver-allocated resources") but the commit itself seems
to be correct.

Fix the issue by dropping the 'hid_dev->driver' override and using
hid_register_driver()/hid_unregister_driver() instead. Alternatively, it
would have been possible to rely on the default handling but
HID_CONNECT_DEFAULT implies HID_CONNECT_HIDRAW and it doesn't seem to work
for mousevsc as-is.

Fixes: 62c68e7cee33 ("HID: ensure timely release of driver-allocated resources")
Suggested-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Changes since v1:
- Keep custom HID driver for mousevsc but do it properly
[Michael Kelley].
- Add 'Fixes:' tag [Saurabh Singh Sengar].
---
 drivers/hid/hid-hyperv.c | 58 ++++++++++++++++++++++++++++------------
 1 file changed, 41 insertions(+), 17 deletions(-)

diff --git a/drivers/hid/hid-hyperv.c b/drivers/hid/hid-hyperv.c
index f33485d83d24..0fb210e40a41 100644
--- a/drivers/hid/hid-hyperv.c
+++ b/drivers/hid/hid-hyperv.c
@@ -422,6 +422,25 @@ static int mousevsc_hid_raw_request(struct hid_device *hid,
 	return 0;
 }
 
+static int mousevsc_hid_probe(struct hid_device *hid_dev, const struct hid_device_id *id)
+{
+	int ret;
+
+	ret = hid_parse(hid_dev);
+	if (ret) {
+		hid_err(hid_dev, "parse failed\n");
+		return ret;
+	}
+
+	ret = hid_hw_start(hid_dev, HID_CONNECT_HIDINPUT | HID_CONNECT_HIDDEV);
+	if (ret) {
+		hid_err(hid_dev, "hw start failed\n");
+		return ret;
+	}
+
+	return 0;
+}
+
 static const struct hid_ll_driver mousevsc_ll_driver = {
 	.parse = mousevsc_hid_parse,
 	.open = mousevsc_hid_open,
@@ -431,7 +450,16 @@ static const struct hid_ll_driver mousevsc_ll_driver = {
 	.raw_request = mousevsc_hid_raw_request,
 };
 
-static struct hid_driver mousevsc_hid_driver;
+static const struct hid_device_id mousevsc_devices[] = {
+	{ HID_DEVICE(BUS_VIRTUAL, HID_GROUP_ANY, 0x045E, 0x0621) },
+	{ }
+};
+
+static struct hid_driver mousevsc_hid_driver = {
+	.name = "hid-hyperv",
+	.id_table = mousevsc_devices,
+	.probe = mousevsc_hid_probe,
+};
 
 static int mousevsc_probe(struct hv_device *device,
 			const struct hv_vmbus_device_id *dev_id)
@@ -473,7 +501,6 @@ static int mousevsc_probe(struct hv_device *device,
 	}
 
 	hid_dev->ll_driver = &mousevsc_ll_driver;
-	hid_dev->driver = &mousevsc_hid_driver;
 	hid_dev->bus = BUS_VIRTUAL;
 	hid_dev->vendor = input_dev->hid_dev_info.vendor;
 	hid_dev->product = input_dev->hid_dev_info.product;
@@ -488,20 +515,6 @@ static int mousevsc_probe(struct hv_device *device,
 	if (ret)
 		goto probe_err2;
 
-
-	ret = hid_parse(hid_dev);
-	if (ret) {
-		hid_err(hid_dev, "parse failed\n");
-		goto probe_err2;
-	}
-
-	ret = hid_hw_start(hid_dev, HID_CONNECT_HIDINPUT | HID_CONNECT_HIDDEV);
-
-	if (ret) {
-		hid_err(hid_dev, "hw start failed\n");
-		goto probe_err2;
-	}
-
 	device_init_wakeup(&device->device, true);
 
 	input_dev->connected = true;
@@ -579,12 +592,23 @@ static struct  hv_driver mousevsc_drv = {
 
 static int __init mousevsc_init(void)
 {
-	return vmbus_driver_register(&mousevsc_drv);
+	int ret;
+
+	ret = hid_register_driver(&mousevsc_hid_driver);
+	if (ret)
+		return ret;
+
+	ret = vmbus_driver_register(&mousevsc_drv);
+	if (ret)
+		hid_unregister_driver(&mousevsc_hid_driver);
+
+	return ret;
 }
 
 static void __exit mousevsc_exit(void)
 {
 	vmbus_driver_unregister(&mousevsc_drv);
+	hid_unregister_driver(&mousevsc_hid_driver);
 }
 
 MODULE_LICENSE("GPL");
-- 
2.47.0