Re: Shutting down a VM with Kernel 4.14 will sometime hang and a reboot is the only way to recover.

[David Hill <dhill@redhat.com>]

On 2017-11-29 09:42 PM, Jason Wang wrote:
>
>
> On 2017年11月30日 03:13, David Hill wrote:
>>
>>
>> On 2017-11-29 12:15 AM, Jason Wang wrote:
>>>
>>>
>>> On 2017年11月29日 10:52, Dave Hill wrote:
>>>>>>
>>>>>
>>>>> Thanks. Zerocopy is disabled by several distribution by default. 
>>>>> For upstream, the only reason to let it on is to hope more 
>>>>> developers can help and fix the issues.
>>>>>
>>>>>
>>>> So I never hit this issue with previous kernel and this issue 
>>>> started happening with the v4.14-rc series.
>>>
>>>
>>> Right, this still need to be investigated if it was introduced 
>>> recently.
>>>
>>> Looking at git history, the only suspected commit is for 4.14 is
>>>
>>> commit 1e6f74536de08b5e50cf0e37e735911c2cef7c62
>>> Author: Willem de Bruijn <willemb@google.com>
>>> Date:   Fri Oct 6 13:22:31 2017 -0400
>>>
>>>     vhost_net: do not stall on zerocopy depletion
>>>
>>> Maybe you can try to revert it and see.
>>>
>>> If it does not solve your issue, I suspect there's bug elsewhere 
>>> that cause a packet to be held for very long time.
>>>
>>>>   I'm using rawhide so perhaps this is why it isn't disabled by 
>>>> default but I have to mention it's an update of FC25 up to FC28 and 
>>>> it never got disabled.
>>>> Perhaps it should be disabled in Fedora too if it's not the case... 
>>>> I'm not sure this is the place to discuss this ... is it? 
>>>
>>> Probably not, but I guess Fedora tries to use new technology 
>>> aggressively.
>>>
>>> Thanks
>>
>> I can revert that commit in 4.15-rc1 but I can't find it in 4.14.2 
>> ...  Is there another commit that could affect this ?
>
> My bad, the suspicious is then:
>
> 1f8b977ab32dc5d148f103326e80d9097f1cefb5 ("sock: enable MSG_ZEROCOPY")
> c1d1b437816f0afa99202be3cb650c9d174667bc ("net: convert (struct 
> ubuf_info)->refcnt to refcount_t")
>
> Thanks
>

Reverting those two commits breaks kernel compilation:

net/core/dev.c: In function ‘dev_queue_xmit_nit’:
net/core/dev.c:1952:8: error: implicit declaration of function 
‘skb_orphan_frags_rx’; did you mean ‘skb_orphan_frags’? 
[-Werror=implicit-function-declaration]
    if (!skb_orphan_frags_rx(skb2, GFP_ATOMIC))
         ^~~~~~~~~~~~~~~~~~~
         skb_orphan_frags


I changed skb_orphan_frags_rx to skb_orphan_frags and it compiled but 
will everything blow up?

Thanks,
Dave