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

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Date:   Mon, 28 Dec 2020 11:58:04 +0000
From:   wangyunjian <wangyunjian@...wei.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
CC:     Network Development <netdev@...r.kernel.org>,
        Jason Wang <jasowang@...hat.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "Lilijun (Jerry)" <jerry.lilijun@...wei.com>,
        chenchanghu <chenchanghu@...wei.com>,
        xudingke <xudingke@...wei.com>,
        "huangbin (J)" <brian.huangbin@...wei.com>
Subject: RE: [PATCH net v5 1/2] vhost_net: fix ubuf refcount incorrectly
 when sendmsg fails

> -----Original Message-----
> From: Willem de Bruijn [mailto:willemdebruijn.kernel@...il.com]
> Sent: Monday, December 28, 2020 12:15 AM
> To: Michael S. Tsirkin <mst@...hat.com>
> Cc: wangyunjian <wangyunjian@...wei.com>; Network Development
> <netdev@...r.kernel.org>; Jason Wang <jasowang@...hat.com>; Willem de
> Bruijn <willemdebruijn.kernel@...il.com>;
> virtualization@...ts.linux-foundation.org; Lilijun (Jerry)
> <jerry.lilijun@...wei.com>; chenchanghu <chenchanghu@...wei.com>;
> xudingke <xudingke@...wei.com>; huangbin (J)
> <brian.huangbin@...wei.com>
> Subject: Re: [PATCH net v5 1/2] vhost_net: fix ubuf refcount incorrectly when
> sendmsg fails
> 
> On Sun, Dec 27, 2020 at 6:26 AM Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> > On Fri, Dec 25, 2020 at 03:24:25PM +0800, wangyunjian wrote:
> > > From: Yunjian Wang <wangyunjian@...wei.com>
> > >
> > > 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")

OK, thanks, I will fix it in next version.

> 
> That introduces the actual block that releases the buffer on error:
> 
> "
>                 err = sock->ops->sendmsg(NULL, sock, &msg, len);
>                 if (unlikely(err < 0)) {
> +                       if (zcopy) {
> +                               if (ubufs)
> +                                       vhost_ubuf_put(ubufs);
> +                               vq->upend_idx =
> ((unsigned)vq->upend_idx - 1) %
> +                                       UIO_MAXIOV;
> +                       }
> "