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Commit 236742de authored by Bernard Blackham's avatar Bernard Blackham Committed by Greg Kroah-Hartman
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staging: usbip: avoid deadlock in vhci_device_unlink_cleanup() 



Almost all of usbip assumes that the_controller->lock is acquired
before vdev->priv_lock. The exception is in
vhci_device_unlink_cleanup(), where locks are acquired in the
reverse order. This leads to occasional deadlocks.

Fixing this is a bit fiddly, as the_controller->lock can't be held
when calling usb_hcd_unlink_urb_from_ep() in the middle of the list
traversal. As I can't rule out concurrent callers to this function
(perhaps it is safe?), the code here becomes slightly uglier - when
locks are dropped in the middle so the list may have emptied itself
(not even list_for_each_entry_safe is safe here).

Signed-off-by: default avatarBernard Blackham <b-linuxgit@largestprime.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 73295fe1

drivers/staging/usbip/vhci_hcd.c

+13 −3
Original line number Diff line number Diff line
@@ -749,6 +749,7 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev) 
{

	struct vhci_unlink *unlink, *tmp;



	spin_lock(&the_controller->lock);

	spin_lock(&vdev->priv_lock);



	list_for_each_entry_safe(unlink, tmp, &vdev->unlink_tx, list) {
@@ -757,9 +758,12 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev) 
		kfree(unlink);

	}



	list_for_each_entry_safe(unlink, tmp, &vdev->unlink_rx, list) {

	while (!list_empty(&vdev->unlink_rx)) {

		struct urb *urb;



		unlink = list_first_entry(&vdev->unlink_rx, struct vhci_unlink,

			list);



		/* give back URB of unanswered unlink request */

		pr_info("unlink cleanup rx %lu\n", unlink->unlink_seqnum);
@@ -774,18 +778,24 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev) 


		urb->status = -ENODEV;



		spin_lock(&the_controller->lock);

		usb_hcd_unlink_urb_from_ep(vhci_to_hcd(the_controller), urb);



		list_del(&unlink->list);



		spin_unlock(&vdev->priv_lock);

		spin_unlock(&the_controller->lock);



		usb_hcd_giveback_urb(vhci_to_hcd(the_controller), urb,

				     urb->status);



		list_del(&unlink->list);

		spin_lock(&the_controller->lock);

		spin_lock(&vdev->priv_lock);



		kfree(unlink);

	}



	spin_unlock(&vdev->priv_lock);

	spin_unlock(&the_controller->lock);

}



/*