Commit 332fa82d authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Michael S. Tsirkin
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Revert "virtio: turn vq->notification into a nested counter" 



This reverts commit aff8fd18.

Both virtio-net and virtio-crypto do not balance
virtio_queue_set_notification() enable and disable calls.  This makes
the notifications_disabled counter unreliable and Doug Goldstein
reported the following assertion failure:

  #3  0x00007ffff44d1c62 in __GI___assert_fail (
      assertion=assertion@entry=0x555555ae8e8a "vq->notification_disabled > 0",
      file=file@entry=0x555555ae89c0 "/home/doug/work/qemu/hw/virtio/virtio.c",
      line=line@entry=215,
      function=function@entry=0x555555ae9630 <__PRETTY_FUNCTION__.43707>
      "virtio_queue_set_notification") at assert.c:101
  #4  0x00005555557f25d6 in virtio_queue_set_notification (vq=0x55555666aa90,
      enable=enable@entry=1) at /home/doug/work/qemu/hw/virtio/virtio.c:215
  #5  0x00005555557dc311 in virtio_net_has_buffers (q=<optimized out>,
      q=<optimized out>, bufsize=102)
      at /home/doug/work/qemu/hw/net/virtio-net.c:1008
  #6  virtio_net_receive (nc=<optimized out>, buf=0x555557386b88 "", size=102)
      at /home/doug/work/qemu/hw/net/virtio-net.c:1148
  #7  0x00005555559cad33 in nc_sendv_compat (flags=<optimized out>, iovcnt=1,
      iov=0x7fffead746d0, nc=0x55555788b340) at net/net.c:705
  #8  qemu_deliver_packet_iov (sender=<optimized out>, flags=<optimized out>,
      iov=0x7fffead746d0, iovcnt=1, opaque=0x55555788b340) at net/net.c:732
  #9  0x00005555559cd929 in qemu_net_queue_deliver (size=<optimized out>,
      data=<optimized out>, flags=<optimized out>, sender=<optimized out>,
      queue=0x55555788b550) at net/queue.c:164
  #10 qemu_net_queue_flush (queue=0x55555788b550) at net/queue.c:261

This patch is safe to revert since it's just an optimization for
virtqueue polling.  The next patch will improve the situation again
without resorting to nesting.

Reported-by: default avatarDoug Goldstein <cardoe@cardoe.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Tested-by: default avatarRichard Henderson <rth@twiddle.net>
Tested-by: default avatarLaszlo Ersek <lersek@redhat.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 4a3f03ba

hw/virtio/virtio.c

+6 −12
Original line number Diff line number Diff line
@@ -88,8 +88,8 @@ struct VirtQueue 
    /* Last used index value we have signalled on */

    bool signalled_used_valid;



    /* Nested host->guest notification disabled counter */

    unsigned int notification_disabled;

    /* Notification enabled? */

    bool notification;



    uint16_t queue_index;
@@ -202,7 +202,7 @@ static inline void vring_used_flags_unset_bit(VirtQueue *vq, int mask) 
static inline void vring_set_avail_event(VirtQueue *vq, uint16_t val)

{

    hwaddr pa;

    if (vq->notification_disabled) {

    if (!vq->notification) {

        return;

    }

    pa = vq->vring.used + offsetof(VRingUsed, ring[vq->vring.num]);
@@ -211,13 +211,7 @@ static inline void vring_set_avail_event(VirtQueue *vq, uint16_t val) 


void virtio_queue_set_notification(VirtQueue *vq, int enable)

{

    if (enable) {

        assert(vq->notification_disabled > 0);

        vq->notification_disabled--;

    } else {

        vq->notification_disabled++;

    }



    vq->notification = enable;

    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {

        vring_set_avail_event(vq, vring_avail_idx(vq));

    } else if (enable) {
@@ -1020,7 +1014,7 @@ void virtio_reset(void *opaque) 
        virtio_queue_set_vector(vdev, i, VIRTIO_NO_VECTOR);

        vdev->vq[i].signalled_used = 0;

        vdev->vq[i].signalled_used_valid = false;

        vdev->vq[i].notification_disabled = 0;

        vdev->vq[i].notification = true;

        vdev->vq[i].vring.num = vdev->vq[i].vring.num_default;

        vdev->vq[i].inuse = 0;

    }
@@ -1831,7 +1825,7 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id) 
        vdev->vq[i].vring.desc = qemu_get_be64(f);

        qemu_get_be16s(f, &vdev->vq[i].last_avail_idx);

        vdev->vq[i].signalled_used_valid = false;

        vdev->vq[i].notification_disabled = 0;

        vdev->vq[i].notification = true;



        if (vdev->vq[i].vring.desc) {

            /* XXX virtio-1 devices */