On Tue, Sep 08, 2020 at 09:00:19PM +0800, Zhu, Lingshan wrote:

On 9/8/2020 8:05 PM, Michael S. Tsirkin wrote:

    On Mon, Sep 07, 2020 at 06:52:19PM +0800, Zhu Lingshan wrote:

        In vhost_vdpa ioctl SET_BACKEND_FEATURES path, currect code
        would try to acquire vhost dev mutex twice
        (first shown in vhost_vdpa_unlocked_ioctl), which can lead
        to a dead lock issue.
        This commit removed mutex operations in vhost_set_backend_features.
        As a compensation for vhost_net, a followinig commit will add
        needed mutex lock/unlock operations in a new function
        vhost_net_set_backend_features() which is a wrap of
        vhost_set_backend_features().

        Signed-off-by: Zhu Lingshan [off-list ref]

    I think you need to squash these two or reorder, we can't first
    make code racy then fix it up.

OK, I will send a V2 series with Jason's fixes tomorrow (handle SET/GET_BACKEND_FEATURES in vhost_vdpa ioctl than vring ioctl).

Thanks,
BR
Zhu Lingshan

this never materialized ...

        ---
         drivers/vhost/vhost.c | 2 --
         1 file changed, 2 deletions(-)

        diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
        index b45519ca66a7..e03c9e6f058f 100644
        --- a/drivers/vhost/vhost.c
        +++ b/drivers/vhost/vhost.c
        @@ -2591,14 +2591,12 @@ void vhost_set_backend_features(struct vhost_dev *dev, u64 features)
                struct vhost_virtqueue *vq;
                int i;

        -       mutex_lock(&dev->mutex);
                for (i = 0; i < dev->nvqs; ++i) {
                        vq = dev->vqs[i];
                        mutex_lock(&vq->mutex);
                        vq->acked_backend_features = features;
                        mutex_unlock(&vq->mutex);
                }
        -       mutex_unlock(&dev->mutex);
         }
         EXPORT_SYMBOL_GPL(vhost_set_backend_features);

        --
        2.18.4