Re: [PATCH net] vhost_net: don't continue to call the recvmsg when meet errors

[Jason Wang]

On 2016å12æ01æ 10:48, wangyunjian wrote:
> > -----Original Message-----
> > From: Michael S. Tsirkin [mailto:mst@xxxxxxxxxx]
> > Sent: Wednesday, November 30, 2016 9:41 PM
> > To: wangyunjian
> > Cc: jasowang@xxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; caihe
> > Subject: Re: [PATCH net] vhost_net: don't continue to call the recvmsg when meet errors
> >
> > On Wed, Nov 30, 2016 at 08:10:57PM +0800, Yunjian Wang wrote:
> > > When we meet an error(err=-EBADFD) recvmsg,
> > How do you get EBADFD? Won't vhost_net_rx_peek_head_len
> > return 0 in this case, breaking the loop?
> We started many guest VMs while attaching/detaching some virtio-net nics for loop.
> The soft lockup might happened. The err is -EBADFD.

How did you do the attaching/detaching? AFAIK, the -EBADFD can only 
happens when you deleting tun device during vhost_net transmission.

> meesage log:
> kernel:[609608.510180]BUG: soft lockup - CPU#18 stuck for 23s! [vhost-60898:126093]
> call trace:
> [<fffffffa0132967>]vhost_get_vq_desc+0x1e7/0x984 [vhost]
> [<fffffffa02037e6>]handle_rx+0x226/0x810 [vhost_net]
> [<fffffffa0203de5>]handle_rx_net+0x15/0x20 [vhost_net]
> [<fffffffa013160b>]vhost_worker+0xfb/0x1e0 [vhost]
> [<fffffffa0131510>]? vhost_dev_reset_owner+0x50/0x50 [vhost]
> [<fffffff810a5c7f>]kthread+0xcf/0xe0
> [<fffffff810a5bb0>]? kthread_create_on_node+0x140/0x140
> [<fffffff81648898>]ret_from_fork+0x58/0x90
> [<fffffff810a5bb0>]? kthread_create_on_node+0x140/0x140
>
> > > the error handling in vhost
> > > handle_rx() will continue. This will cause a soft CPU lockup in vhost thread.
> > >
> > > Signed-off-by: Yunjian Wang <wangyunjian@xxxxxxxxxx>
> > > ---
> > >   drivers/vhost/net.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > > index 5dc128a..edc470b 100644
> > > --- a/drivers/vhost/net.c
> > > +++ b/drivers/vhost/net.c
> > > @@ -717,6 +717,9 @@ static void handle_rx(struct vhost_net *net)
> > >   			pr_debug("Discarded rx packet: "
> > >   				 " len %d, expected %zd\n", err, sock_len);
> > >   			vhost_discard_vq_desc(vq, headcount);
> > > +			/* Don't continue to do, when meet errors. */
> > > +			if (err < 0)
> > > +				goto out;
> > You might get e.g. EAGAIN and I think you need to retry
> > in this case.
> >
> > >   			continue;
> > >   		}
> > >   		/* Supply virtio_net_hdr if VHOST_NET_F_VIRTIO_NET_HDR */
> > > --
> > > 1.9.5.msysgit.1