vfio/pci: Clear error and request eventfd ctx after releasing

stable inclusion
from linux-4.19.149
commit 41a77298809e7be112f91972d794aa231fbe27aa

--------------------------------

[ Upstream commit 5c5866c5 ]

The next use of the device will generate an underflow from the
stale reference.

Cc: Qian Cai <cai@lca.pw>
Fixes: 1518ac27 ("vfio/pci: fix memory leaks of eventfd ctx")
Reported-by: NDaniel Wagner <dwagner@suse.de>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Tested-by: NDaniel Wagner <dwagner@suse.de>
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/vfio/pci/vfio_pci.c

@@ -409,10 +409,14 @@ static void vfio_pci_release(void *device_data)
 	if (!(--vdev->refcnt)) {
 		vfio_spapr_pci_eeh_release(vdev->pdev);
 		vfio_pci_disable(vdev);
-		if (vdev->err_trigger)
+		if (vdev->err_trigger) {
 			eventfd_ctx_put(vdev->err_trigger);
-		if (vdev->req_trigger)
+			vdev->err_trigger = NULL;
+		}
+		if (vdev->req_trigger) {
 			eventfd_ctx_put(vdev->req_trigger);
+			vdev->req_trigger = NULL;
+		}
 	}
 
 	mutex_unlock(&driver_lock);