On Thu, Jun 02, 2016 at 08:39:36AM +0000, Xie, Huawei wrote: > On 6/1/2016 2:03 PM, Yuanhan Liu wrote: > > On Wed, Jun 01, 2016 at 05:40:08AM +0000, Xie, Huawei wrote: > >> On 5/30/2016 4:20 PM, Yuanhan Liu wrote: > >>> On Wed, May 25, 2016 at 12:16:41AM +0800, Huawei Xie wrote: > >>>> There is no external function call or any barrier in the loop, > >>>> the used->idx would only be retrieved once. > >>>> > >>>> Signed-off-by: Huawei Xie <huawei.xie at intel.com> > >>>> --- > >>>> drivers/net/virtio/virtio_ethdev.c | 3 ++- > >>>> 1 file changed, 2 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/drivers/net/virtio/virtio_ethdev.c > >>>> b/drivers/net/virtio/virtio_ethdev.c > >>>> index c3fb628..f6d6305 100644 > >>>> --- a/drivers/net/virtio/virtio_ethdev.c > >>>> +++ b/drivers/net/virtio/virtio_ethdev.c > >>>> @@ -204,7 +204,8 @@ virtio_send_command(struct virtqueue *vq, struct > >>>> virtio_pmd_ctrl *ctrl, > >>>> usleep(100); > >>>> } > >>>> > >>>> - while (vq->vq_used_cons_idx != vq->vq_ring.used->idx) { > >>>> + while (vq->vq_used_cons_idx != > >>>> + *((volatile uint16_t *)(&vq->vq_ring.used->idx))) { > >>> I'm wondering maybe we could fix VIRTQUEUE_NUSED (which has no such > >>> qualifier) and use this macro here? > >>> > >>> If you check the reference of that macro, you might find similar > >>> issues, say, it is also used inside the while-loop of > >>> virtio_recv_mergeable_pkts(). > >>> > >>> --yliu > >>> > >>> > >> Yes, seems it has same issue though haven't confirmed with asm code. > > So, move the "volatile" qualifier to VIRTQUEUE_NUSED? > > > > --yliu > > > > Yes, anyway this is just intermediate fix. In next patch, will declare > the idx as volatile, and remove the qualifier in the macro.
Hmm.., why we need an intermediate fix then, if we can come up with an ultimate fix very quickly? --yliu