vfio-pci: Avoid deadlock on remove

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>

1 files changed, 21 insertions, 2 deletions

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index c5179e269df6..cef6002acbd4 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);
 }