[PATCH v3 1/2] usbip: give back URBs for unsent unlink requests during cleanup

[Anirudh Rayabharam <mail@anirudhrb.com>]

In vhci_device_unlink_cleanup(), the URBs for unsent unlink requests are
not given back. This sometimes causes usb_kill_urb to wait indefinitely
for that urb to be given back. syzbot has reported a hung task issue [1]
for this.

To fix this, give back the urbs corresponding to unsent unlink requests
(unlink_tx list) similar to how urbs corresponding to unanswered unlink
requests (unlink_rx list) are given back.

[1]: https://syzkaller.appspot.com/bug?id=08f12df95ae7da69814e64eb5515d5a85ed06b76

Reported-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
Tested-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
---
 drivers/usb/usbip/vhci_hcd.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
index 4ba6bcdaa8e9..6f3f374d4bbc 100644
--- a/drivers/usb/usbip/vhci_hcd.c
+++ b/drivers/usb/usbip/vhci_hcd.c
@@ -957,8 +957,34 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
 	spin_lock(&vdev->priv_lock);
 
 	list_for_each_entry_safe(unlink, tmp, &vdev->unlink_tx, list) {
+		struct urb *urb;
+
+		/* give back URB of unsent unlink request */
 		pr_info("unlink cleanup tx %lu\n", unlink->unlink_seqnum);
+
+		urb = pickup_urb_and_free_priv(vdev, unlink->unlink_seqnum);
+		if (!urb) {
+			pr_info("the urb (seqnum %lu) was already given back\n",
+				unlink->unlink_seqnum);
+			list_del(&unlink->list);
+			kfree(unlink);
+			continue;
+		}
+
+		urb->status = -ENODEV;
+
+		usb_hcd_unlink_urb_from_ep(hcd, urb);
+
 		list_del(&unlink->list);
+
+		spin_unlock(&vdev->priv_lock);
+		spin_unlock_irqrestore(&vhci->lock, flags);
+
+		usb_hcd_giveback_urb(hcd, urb, urb->status);
+
+		spin_lock_irqsave(&vhci->lock, flags);
+		spin_lock(&vdev->priv_lock);
+
 		kfree(unlink);
 	}
 
-- 
2.26.2