vfio-pci: Don't use device_lock around AER interrupt setup

device_lock is much too prone to lockups.  For instance if we have a
pending .remove then device_lock is already held.  If userspace
attempts to modify AER signaling after that point, a deadlock occurs.
eventfd setup/teardown is already protected in vfio with the igate
mutex.  AER is not a high performance interrupt, so we can also use
the same mutex to protect signaling versus setup races.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/vfio_pci.c

@@ -883,9 +883,13 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
 		return PCI_ERS_RESULT_DISCONNECT;
 	}
 
+	mutex_lock(&vdev->igate);
+
 	if (vdev->err_trigger)
 		eventfd_signal(vdev->err_trigger, 1);
 
+	mutex_unlock(&vdev->igate);
+
 	vfio_device_put(device);
 
 	return PCI_ERS_RESULT_CAN_RECOVER;

drivers/vfio/pci/vfio_pci_intrs.c

@@ -749,54 +749,37 @@ static int vfio_pci_set_err_trigger(struct vfio_pci_device *vdev,
 				    unsigned count, uint32_t flags, void *data)
 {
 	int32_t fd = *(int32_t *)data;
-	struct pci_dev *pdev = vdev->pdev;
 
 	if ((index != VFIO_PCI_ERR_IRQ_INDEX) ||
 	    !(flags & VFIO_IRQ_SET_DATA_TYPE_MASK))
 		return -EINVAL;
 
-	/*
-	 * device_lock synchronizes setting and checking of
-	 * err_trigger. The vfio_pci_aer_err_detected() is also
-	 * called with device_lock held.
-	 */
-
 	/* DATA_NONE/DATA_BOOL enables loopback testing */
-
 	if (flags & VFIO_IRQ_SET_DATA_NONE) {
-		device_lock(&pdev->dev);
 		if (vdev->err_trigger)
 			eventfd_signal(vdev->err_trigger, 1);
-		device_unlock(&pdev->dev);
 		return 0;
 	} else if (flags & VFIO_IRQ_SET_DATA_BOOL) {
 		uint8_t trigger = *(uint8_t *)data;
-		device_lock(&pdev->dev);
 		if (trigger && vdev->err_trigger)
 			eventfd_signal(vdev->err_trigger, 1);
-		device_unlock(&pdev->dev);
 		return 0;
 	}
 
 	/* Handle SET_DATA_EVENTFD */
-
 	if (fd == -1) {
-		device_lock(&pdev->dev);
 		if (vdev->err_trigger)
 			eventfd_ctx_put(vdev->err_trigger);
 		vdev->err_trigger = NULL;
-		device_unlock(&pdev->dev);
 		return 0;
 	} else if (fd >= 0) {
 		struct eventfd_ctx *efdctx;
 		efdctx = eventfd_ctx_fdget(fd);
 		if (IS_ERR(efdctx))
 			return PTR_ERR(efdctx);
-		device_lock(&pdev->dev);
 		if (vdev->err_trigger)
 			eventfd_ctx_put(vdev->err_trigger);
 		vdev->err_trigger = efdctx;
-		device_unlock(&pdev->dev);
 		return 0;
 	} else
 		return -EINVAL;