vfio: Fix runaway interruptible timeout

awilliam · awilliam · commit db7d4d7f4021 · 2015-05-01T16:31:41.000-06:00
Commit 13060b6 ("vfio: Add and use device request op for vfio bus drivers") incorrectly makes use of an interruptible timeout. When interrupted, the signal remains pending resulting in subsequent timeouts occurring instantly. This makes the loop spin at a much higher rate than intended. Instead of making this completely non-interruptible, we can change this into a sort of interruptible-once behavior and use the "once" to log debug information. The driver API doesn't allow us to abort and return an error code. Signed-off-by: Alex Williamson <alex.williamson@redhat.com> Fixes: 13060b6 Cc: stable@vger.kernel.org # v4.0
diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
@@ -710,6 +710,8 @@ void *vfio_del_group_dev(struct device *dev)
 	void *device_data = device->device_data;
 	struct vfio_unbound_dev *unbound;
 	unsigned int i = 0;
+	long ret;
+	bool interrupted = false;
 
 	/*
 	 * The group exists so long as we have a device reference.  Get
@@ -755,9 +757,22 @@ void *vfio_del_group_dev(struct device *dev)
 
 		vfio_device_put(device);
 
-	} while (wait_event_interruptible_timeout(vfio.release_q,
-						  !vfio_dev_present(group, dev),
-						  HZ * 10) <= 0);
+		if (interrupted) {
+			ret = wait_event_timeout(vfio.release_q,
+					!vfio_dev_present(group, dev), HZ * 10);
+		} else {
+			ret = wait_event_interruptible_timeout(vfio.release_q,
+					!vfio_dev_present(group, dev), HZ * 10);
+			if (ret == -ERESTARTSYS) {
+				interrupted = true;
+				dev_warn(dev,
+					 "Device is currently in use, task"
+					 " \"%s\" (%d) "
+					 "blocked until device is released",
+					 current->comm, task_pid_nr(current));
+			}
+		}
+	} while (ret <= 0);
 
 	vfio_group_put(group);
 
