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 2017-11-30 03:52 PM, David Hill wrote:
>
>
> 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

Finally, I reverted 581fe0ea61584d88072527ae9fb9dcb9d1f2783e too ... 
compiling and I'll keep you posted.