[dpdk-dev] [PATCH v4 1/2] net/virtio: check head desc with correct wrap counter

[Jens Freimann]

In virtio_pq_send_command() we check for a used descriptor
and wait in an idle loop until it becomes used. We can't use
vq->used_wrap_counter here to check for the first descriptor
we made available because the ring could have wrapped. Let's use
the used_wrap_counter that matches the state of the head descriptor.

Fixes: ec194c2 ("net/virtio: support packed queue in send command")

Signed-off-by: Jens Freimann <jfreim...@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coque...@redhat.com>
---
 drivers/net/virtio/virtio_ethdev.c | 11 ++++++-----
 drivers/net/virtio/virtqueue.h     | 10 ++++++++--
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/net/virtio/virtio_ethdev.c 
b/drivers/net/virtio/virtio_ethdev.c
index 6d461180c..ee5a98b7c 100644
--- a/drivers/net/virtio/virtio_ethdev.c
+++ b/drivers/net/virtio/virtio_ethdev.c
@@ -149,7 +149,7 @@ virtio_pq_send_command(struct virtnet_ctl *cvq, struct 
virtio_pmd_ctrl *ctrl,
        int head;
        struct vring_packed_desc *desc = vq->ring_packed.desc_packed;
        struct virtio_pmd_ctrl *result;
-       int wrap_counter;
+       bool avail_wrap_counter, used_wrap_counter;
        uint16_t flags;
        int sum = 0;
        int k;
@@ -161,7 +161,8 @@ virtio_pq_send_command(struct virtnet_ctl *cvq, struct 
virtio_pmd_ctrl *ctrl,
         * One RX packet for ACK.
         */
        head = vq->vq_avail_idx;
-       wrap_counter = vq->avail_wrap_counter;
+       avail_wrap_counter = vq->avail_wrap_counter;
+       used_wrap_counter = vq->used_wrap_counter;
        desc[head].flags = VRING_DESC_F_NEXT;
        desc[head].addr = cvq->virtio_net_hdr_mem;
        desc[head].len = sizeof(struct virtio_net_ctrl_hdr);
@@ -199,8 +200,8 @@ virtio_pq_send_command(struct virtnet_ctl *cvq, struct 
virtio_pmd_ctrl *ctrl,
                 VRING_DESC_F_USED(!vq->avail_wrap_counter);
        desc[vq->vq_avail_idx].flags = flags;
        flags = VRING_DESC_F_NEXT;
-       flags |= VRING_DESC_F_AVAIL(wrap_counter) |
-                VRING_DESC_F_USED(!wrap_counter);
+       flags |= VRING_DESC_F_AVAIL(avail_wrap_counter) |
+                VRING_DESC_F_USED(!avail_wrap_counter);
        desc[head].flags = flags;
        rte_smp_wmb();
 
@@ -216,7 +217,7 @@ virtio_pq_send_command(struct virtnet_ctl *cvq, struct 
virtio_pmd_ctrl *ctrl,
        do {
                rte_rmb();
                usleep(100);
-       } while (!desc_is_used(&desc[head], vq));
+       } while (!__desc_is_used(&desc[head], used_wrap_counter));
 
        /* now get used descriptors */
        while (desc_is_used(&desc[vq->vq_used_cons_idx], vq)) {
diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
index 123bec34f..7fcde5643 100644
--- a/drivers/net/virtio/virtqueue.h
+++ b/drivers/net/virtio/virtqueue.h
@@ -281,7 +281,7 @@ struct virtio_tx_region {
 };
 
 static inline int
-desc_is_used(struct vring_packed_desc *desc, struct virtqueue *vq)
+__desc_is_used(struct vring_packed_desc *desc, bool wrap_counter)
 {
        uint16_t used, avail, flags;
 
@@ -289,7 +289,13 @@ desc_is_used(struct vring_packed_desc *desc, struct 
virtqueue *vq)
        used = !!(flags & VRING_DESC_F_USED(1));
        avail = !!(flags & VRING_DESC_F_AVAIL(1));
 
-       return avail == used && used == vq->used_wrap_counter;
+       return avail == used && used == wrap_counter;
+}
+
+static inline int
+desc_is_used(struct vring_packed_desc *desc, struct virtqueue *vq)
+{
+       return __desc_is_used(desc, vq->used_wrap_counter);
 }
 
 
-- 
2.17.2