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.