Re: [PATCH 5/6] vhost_net: poll vhost queue after marking DMA is done
flat view
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2013-08-16 09:59:14
Also in:
kvm, lkml, netdev
On Fri, Aug 16, 2013 at 01:16:29PM +0800, Jason Wang wrote:
We used to poll vhost queue before making DMA is done, this is racy if vhost thread were waked up before marking DMA is done which can result the signal to be missed. Fix this by always poll the vhost thread before DMA is done. Signed-off-by: Jason Wang <redacted>
Indeed, but vhost_net_ubuf_put should be the last thing we do: it can cause the device to go away and we'll get a user after free.
quoted hunk ↗ jump to hunk
--- drivers/vhost/net.c | 9 +++++---- 1 files changed, 5 insertions(+), 4 deletions(-)diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 70cab75..a035a89 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c@@ -308,6 +308,11 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) struct vhost_virtqueue *vq = ubufs->vq; int cnt = atomic_read(&ubufs->kref.refcount); + /* set len to mark this desc buffers done DMA */ + vq->heads[ubuf->desc].len = success ? + VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN; + vhost_net_ubuf_put(ubufs); + /* * Trigger polling thread if guest stopped submitting new buffers: * in this case, the refcount after decrement will eventually reach 1@@ -318,10 +323,6 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) */ if (cnt <= 2 || !(cnt % 16)) vhost_poll_queue(&vq->poll); - /* set len to mark this desc buffers done DMA */ - vq->heads[ubuf->desc].len = success ? - VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN; - vhost_net_ubuf_put(ubufs); } /* Expects to be always run from workqueue - which acts as-- 1.7.1