Messages in this thread | | | Subject | Re: [PATCH 3/4] vsock/virtio: fix flush of works during the .remove() | From | Jason Wang <> | Date | Thu, 30 May 2019 17:46:18 +0800 |
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On 2019/5/29 下午6:58, Stefano Garzarella wrote: > On Wed, May 29, 2019 at 11:22:40AM +0800, Jason Wang wrote: >> 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 <mst@redhat.com> >>> Signed-off-by: Stefano Garzarella <sgarzare@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? >> > Both virtio_transport_send_pkt() and vsock_transport_cancel_pkt() can > queue work from the upper layer (socket). > > Setting the_virtio_vsock to NULL, should synchronize, but after a careful look > a rare issue could happen: > we are setting the_virtio_vsock to NULL at the start of .remove() and we > are freeing the object pointed by it at the end of .remove(), so > virtio_transport_send_pkt() or vsock_transport_cancel_pkt() may still be > running, accessing the object that we are freed.
Yes, that's my point.
> > Should I use something like RCU to prevent this issue? > > virtio_transport_send_pkt() and vsock_transport_cancel_pkt() > { > rcu_read_lock(); > vsock = rcu_dereference(the_virtio_vsock_mutex);
RCU is probably a way to go. (Like what vhost_transport_send_pkt() did).
> ... > rcu_read_unlock(); > } > > virtio_vsock_remove() > { > rcu_assign_pointer(the_virtio_vsock_mutex, NULL); > synchronize_rcu(); > > ... > > free(vsock); > } > > Could there be a better approach? > > >> 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. > The main reason of tx_run/rx_run/event_run is to prevent that a worker > function is running while we are calling config->reset(). > > E.g. if an interrupt comes between virtio_vsock_flush_works() and > config->reset(), it can queue new works that can access the device while > we are in config->reset(). > > IMHO they are still needed. > > What do you think?
I mean could we simply do flush after reset once and without tx_rx/rx_run tricks?
rest();
virtio_vsock_flush_work();
virtio_vsock_free_buf();
Thanks
> > > Thanks for your questions, > Stefano
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