Re: [PATCH 3/4] vsock/virtio: fix flush of works during the .remove()

[Jason Wang]

On 2019/5/28 下午6:56, Stefano Garzarella wrote:
We flush all pending works before to call vdev->config->reset(vdev),
but other works can be queued before the vdev->config->del_vqs(vdev),
so we add another flush after it, to avoid use after free.

Suggested-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Stefano Garzarella <sgarz...@redhat.com>
---
  net/vmw_vsock/virtio_transport.c | 23 +++++++++++++++++------
  1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index e694df10ab61..ad093ce96693 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -660,6 +660,15 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
        return ret;
  }
  
+static void virtio_vsock_flush_works(struct virtio_vsock *vsock)
+{
+       flush_work(&vsock->loopback_work);
+       flush_work(&vsock->rx_work);
+       flush_work(&vsock->tx_work);
+       flush_work(&vsock->event_work);
+       flush_work(&vsock->send_pkt_work);
+}
+
  static void virtio_vsock_remove(struct virtio_device *vdev)
  {
        struct virtio_vsock *vsock = vdev->priv;
@@ -668,12 +677,6 @@ static void virtio_vsock_remove(struct virtio_device *vdev)
        mutex_lock(&the_virtio_vsock_mutex);
        the_virtio_vsock = NULL;
  
-	flush_work(&vsock->loopback_work);
-       flush_work(&vsock->rx_work);
-       flush_work(&vsock->tx_work);
-       flush_work(&vsock->event_work);
-       flush_work(&vsock->send_pkt_work);
-
        /* Reset all connected sockets when the device disappear */
        vsock_for_each_connected_socket(virtio_vsock_reset_sock);
  
@@ -690,6 +693,9 @@ static void virtio_vsock_remove(struct virtio_device *vdev)
        vsock->event_run = false;
        mutex_unlock(&vsock->event_lock);
  
+	/* Flush all pending works */
+       virtio_vsock_flush_works(vsock);
+
        /* Flush all device writes and interrupts, device will not use any
         * more buffers.
         */
@@ -726,6 +732,11 @@ static void virtio_vsock_remove(struct virtio_device *vdev)
        /* Delete virtqueues and flush outstanding callbacks if any */
        vdev->config->del_vqs(vdev);
  
+	/* Other works can be queued before 'config->del_vqs()', so we flush
+        * all works before to free the vsock object to avoid use after free.
+        */
+       virtio_vsock_flush_works(vsock);


Some questions after a quick glance:

1) It looks to me that the work could be queued from the path of 
vsock_transport_cancel_pkt() . Is that synchronized here?

2) If we decide to flush after dev_vqs(), is tx_run/rx_run/event_run 
still needed? It looks to me we've already done except that we need 
flush rx_work in the end since send_pkt_work can requeue rx_work.

Thanks


+
        kfree(vsock);
        mutex_unlock(&the_virtio_vsock_mutex);
  }