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Re: [Qemu-devel] [PATCH] clean up callback when del virtqueue

From: Jason Wang
Subject: Re: [Qemu-devel] [PATCH] clean up callback when del virtqueue
Date: Fri, 14 Sep 2018 20:44:30 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 2018年09月08日 21:04, liujunjie wrote:
Before, we did not clear callback like handle_output when delete
the virtqueue which may result be segmentfault.
The scene is as follows:
1. Start a vm with multiqueue vhost-net,
2. then we write VIRTIO_PCI_GUEST_FEATURES in PCI configuration to
triger multiqueue disable in this vm which will delete the virtqueue.
In this step, the tx_bh is deleted but the callback virtio_net_handle_tx_bh
still exist.
3. Finally, we write VIRTIO_PCI_QUEUE_NOTIFY in PCI configuration to
notify the deleted virtqueue. In this way, virtio_net_handle_tx_bh
will be called and qemu will be crashed.

Good catch.

Although the way described above is uncommon, we had better reinforce it.

Signed-off-by: liujunjie <address@hidden>
  hw/net/virtio-net.c | 4 +++-
  hw/virtio/virtio.c  | 3 +++
  2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index f154756..9bb20e3 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1467,7 +1467,9 @@ static void virtio_net_handle_tx_bh(VirtIODevice *vdev, 
VirtQueue *vq)
      virtio_queue_set_notification(vq, 0);
-    qemu_bh_schedule(q->tx_bh);
+    if (q->tx_bh) {
+        qemu_bh_schedule(q->tx_bh);
+    }

I believe this is not necessary since handle_output is NULL now?

static void virtio_net_tx_timer(void *opaque)
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index d4e4d98..7577518 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -1604,6 +1604,9 @@ void virtio_del_queue(VirtIODevice *vdev, int n)
vdev->vq[n].vring.num = 0;
      vdev->vq[n].vring.num_default = 0;
+    vdev->vq[n].vring.align = 0;

Is this related or fix for another bug?


+    vdev->vq[n].handle_output = NULL;
+    vdev->vq[n].handle_aio_output = NULL;
static void virtio_set_isr(VirtIODevice *vdev, int value)

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