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

[Jason Wang <jasowang@redhat.com>]

On 2016年12月01日 10:48, wangyunjian wrote:
>> -----Original Message-----
>> From: Michael S. Tsirkin [mailto:mst@redhat.com]
>> Sent: Wednesday, November 30, 2016 9:41 PM
>> To: wangyunjian
>> Cc: jasowang@redhat.com; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; 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@huawei.com>
>>> ---
>>>   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
>>>