On 08/16/2013 06:00 PM, Michael S. Tsirkin wrote: > 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 <jasowang@xxxxxxxxxx> > 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. Didn't get this. We didn't use ubuf in vhost_zerocopy_signal_used(), looks safe here? > >> --- >> 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 > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
