[PATCH 3/3] vfio-pci: Avoid deadlock on remove

[Alex Williamson <alex.williamson@redhat.com>]

If an attempt is made to unbind a device from vfio-pci while that
device is in use, the request is blocked until the device becomes
unused.  Unfortunately, that unbind path still grabs the device_lock,
which certain things like __pci_reset_function() also want to take.
This means we need to try to acquire the locks ourselves and use the
pre-locked version, __pci_reset_function_locked().

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/vfio/pci/vfio_pci.c |   23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index ac37254..41023e4 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -137,8 +137,27 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
 	 */
 	pci_write_config_word(pdev, PCI_COMMAND, PCI_COMMAND_INTX_DISABLE);
 
-	if (vdev->reset_works)
-		__pci_reset_function(pdev);
+	/*
+	 * Careful, device_lock may already be held.  This is the case if
+	 * a driver unbind is blocked.  Try to get the locks ourselves to
+	 * prevent a deadlock.
+	 */
+	if (vdev->reset_works) {
+		bool reset_done = false;
+
+		if (pci_cfg_access_trylock(pdev)) {
+			if (device_trylock(&pdev->dev)) {
+				__pci_reset_function_locked(pdev);
+				reset_done = true;
+				device_unlock(&pdev->dev);
+			}
+			pci_cfg_access_unlock(pdev);
+		}
+
+		if (!reset_done)
+			pr_warn("%s: Unable to acquire locks for reset of %s\n",
+				__func__, dev_name(&pdev->dev));
+	}
 
 	pci_restore_state(pdev);
 }