On 08/31/2013 12:44 AM, Ben Hutchings wrote:

On Fri, 2013-08-30 at 12:29 +0800, Jason Wang wrote:

quoted

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.

Does this bug only exist in net-next or is it older?  Should the fix go
to net and stable branches?

This should go for the stable branches too (3.4 above).

Thanks for the checking.

Ben.

quoted

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 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 ff60c2a..d09c17c 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