Re: [PATCH net v5 1/2] vhost_net: fix ubuf refcount incorrectly when sendmsg fails

[Willem de Bruijn]

On Sun, Dec 27, 2020 at 6:26 AM Michael S. Tsirkin  wrote:
>
> On Fri, Dec 25, 2020 at 03:24:25PM +0800, wangyunjian wrote:
> > From: Yunjian Wang 
> >
> > Currently the vhost_zerocopy_callback() maybe be called to decrease
> > the refcount when sendmsg fails in tun. The error handling in vhost
> > handle_tx_zerocopy() will try to decrease the same refcount again.
> > This is wrong. To fix this issue, we only call vhost_net_ubuf_put()
> > when vq->heads[nvq->desc].len == VHOST_DMA_IN_PROGRESS.
> >
> > Fixes: 0690899b4d45 ("tun: experimental zero copy tx support")
>
> Are you sure about this tag? the patch in question only affects
> tun, while the fix only affects vhost.

That was my suggestion. But you're right. Perhaps better:

Fixes: bab632d69ee4 ("vhost: vhost TX zero-copy support")

That introduces the actual block that releases the buffer on error:

"
err = sock->ops->sendmsg(NULL, sock, , len);
if (unlikely(err < 0)) {
+   if (zcopy) {
+   if (ubufs)
+   vhost_ubuf_put(ubufs);
+   vq->upend_idx = ((unsigned)vq->upend_idx - 1) %
+   UIO_MAXIOV;
+   }
"
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Re: [PATCH net v5 1/2] vhost_net: fix ubuf refcount incorrectly when sendmsg fails

[Michael S. Tsirkin]

On Fri, Dec 25, 2020 at 03:24:25PM +0800, wangyunjian wrote:
> From: Yunjian Wang 
> 
> Currently the vhost_zerocopy_callback() maybe be called to decrease
> the refcount when sendmsg fails in tun. The error handling in vhost
> handle_tx_zerocopy() will try to decrease the same refcount again.
> This is wrong. To fix this issue, we only call vhost_net_ubuf_put()
> when vq->heads[nvq->desc].len == VHOST_DMA_IN_PROGRESS.
> 
> Fixes: 0690899b4d45 ("tun: experimental zero copy tx support")

Are you sure about this tag? the patch in question only affects
tun, while the fix only affects vhost.

> Signed-off-by: Yunjian Wang 
> Acked-by: Willem de Bruijn 
> Acked-by: Michael S. Tsirkin 
> Acked-by: Jason Wang 
> ---
>  drivers/vhost/net.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 531a00d703cd..c8784dfafdd7 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -863,6 +863,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, 
> struct socket *sock)
>   size_t len, total_len = 0;
>   int err;
>   struct vhost_net_ubuf_ref *ubufs;
> + struct ubuf_info *ubuf;
>   bool zcopy_used;
>   int sent_pkts = 0;
>  
> @@ -895,9 +896,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, 
> struct socket *sock)
>  
>   /* use msg_control to pass vhost zerocopy ubuf info to skb */
>   if (zcopy_used) {
> - struct ubuf_info *ubuf;
>   ubuf = nvq->ubuf_info + nvq->upend_idx;
> -
>   vq->heads[nvq->upend_idx].id = cpu_to_vhost32(vq, head);
>   vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
>   ubuf->callback = vhost_zerocopy_callback;
> @@ -927,7 +926,8 @@ static void handle_tx_zerocopy(struct vhost_net *net, 
> struct socket *sock)
>   err = sock->ops->sendmsg(sock, , len);
>   if (unlikely(err < 0)) {
>   if (zcopy_used) {
> - vhost_net_ubuf_put(ubufs);
> + if (vq->heads[ubuf->desc].len == 
> VHOST_DMA_IN_PROGRESS)
> + vhost_net_ubuf_put(ubufs);
>   nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
>   % UIO_MAXIOV;
>   }
> -- 
> 2.23.0

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