svn commit: r341586 - head/sys/dev/mlx5/mlx5_en

[John Baldwin]

On 4/25/19 12:10 AM, Slava Shwartsman wrote:
> 
> 
> On 17-Apr-19 00:28, John Baldwin wrote:
>> On 4/16/19 8:32 AM, Hans Petter Selasky wrote:
>>> On 4/16/19 4:39 PM, Andrey V. Elsukov wrote:
>>>> On 05.12.2018 17:25, Slava Shwartsman wrote:
>>>>> Author: slavash
>>>>> Date: Wed Dec  5 14:25:03 2018
>>>>> New Revision: 341586
>>>>> URL: https://svnweb.freebsd.org/changeset/base/341586
>>>>>
>>>>> Log:
>>>>>     mlx5en: Implement backpressure indication.
>>>>>     
>>>>>     The backpressure indication is implemented using an unlimited rate type of
>>>>>     mbuf send tag. When the upper layers typically the socket layer has obtained such
>>>>>     a tag, it can then query the destination driver queue for the current
>>>>>     amount of space available in the send queue.
>>>>>     
>>>>>     A single mbuf send tag may be referenced multiple times and a refcount has been added
>>>>>     to the mlx5e_priv structure to track its usage. Because the send tag resides
>>>>>     in the mlx5e_channel structure, there is no need to wait for refcounts to reach
>>>>>     zero until the mlx4en(4) driver is detached. The channels structure is persistant
>>>>>     during the lifetime of the mlx5en(4) driver it belongs to and can so be accessed
>>>>>     without any need of synchronization.
>>>>>     
>>>>>     The mlx5e_snd_tag structure was extended to contain a type field, because there are now
>>>>>     two different tag types which end up in the driver which need to be distinguished.
>>>>>     
>>>>>     Submitted by:   hselasky@
>>>>>     Approved by:    hselasky (mentor)
>>>>>     MFC after:      1 week
>>>>>     Sponsored by:   Mellanox Technologies
>>>>> @@ -587,27 +609,33 @@ mlx5e_xmit(struct ifnet *ifp, struct mbuf *mb)
>>>>>    	struct mlx5e_sq *sq;
>>>>>    	int ret;
>>>>>    
>>>>> -	sq = mlx5e_select_queue(ifp, mb);
>>>>> -	if (unlikely(sq == NULL)) {
>>>>> -#ifdef RATELIMIT
>>>>> -		/* Check for route change */
>>>>> -		if (mb->m_pkthdr.snd_tag != NULL &&
>>>>> -		    mb->m_pkthdr.snd_tag->ifp != ifp) {
>>>>> +	if (mb->m_pkthdr.snd_tag != NULL) {
>>>>> +		sq = mlx5e_select_queue_by_send_tag(ifp, mb);
>>>>> +		if (unlikely(sq == NULL)) {
>>>>> +			/* Check for route change */
>>>>> +			if (mb->m_pkthdr.snd_tag->ifp != ifp) {
>>>>> +				/* Free mbuf */
>>>>> +				m_freem(mb);
>>>>> +
>>>>> +				/*
>>>>> +				 * Tell upper layers about route
>>>>> +				 * change and to re-transmit this
>>>>> +				 * packet:
>>>>> +				 */
>>>>> +				return (EAGAIN);
>>>>> +			}
>>>>
>>>> Hi,
>>>>
>>>> I just discovered something strange and found that this commit is the
>>>> cause.
>>>> The test system has mlx5en 100G interface. It has two vlans: vlan500 and
>>>> vlan100.
>>>> Via vlan500 it receives some packets flows. Then it routes these packets
>>>> into vlan100.
>>>> But packets are dropped in mlx5e_xmit() with EAGAIN error code.
>>>>
>>>> # dtrace -n 'fbt::ip6_output:return {printf("%d", arg1);}'
>>>> dtrace: description 'fbt::ip6_output:return ' matched 1 probe
>>>> CPU     ID                    FUNCTION:NAME
>>>>    23  54338                ip6_output:return 35
>>>>    16  54338                ip6_output:return 35
>>>>    21  54338                ip6_output:return 35
>>>>    22  54338                ip6_output:return 35
>>>>    24  54338                ip6_output:return 35
>>>>    23  54338                ip6_output:return 35
>>>>    14  54338                ip6_output:return 35
>>>> ^C
>>>>
>>>> # dtrace -n 'fbt::mlx5e_xmit:return {printf("%d", arg1);}'
>>>> dtrace: description 'fbt::mlx5e_xmit:return ' matched 1 probe
>>>> CPU     ID                    FUNCTION:NAME
>>>>    16  69030                mlx5e_xmit:return 35
>>>>    23  69030                mlx5e_xmit:return 35
>>>>    26  69030                mlx5e_xmit:return 35
>>>>    25  69030                mlx5e_xmit:return 35
>>>>    24  69030                mlx5e_xmit:return 35
>>>>    21  69030                mlx5e_xmit:return 35
>>>>    26  69030                mlx5e_xmit:return 35
>>>> ^C
>>>>
>>>> The kernel config is GENERIC.
>>>> 13.0-CURRENT #9 r345758+82f3d57(svn_head)-dirty
>>>>
>>>
>>> Hi,
>>>
>>> This might be a case where rcvif in the mbuf's pktheader is not cleared
>>> before the packet is fed back on the wire.
>>>
>>> John Baldwin is working on the send tags implementation, to eliminate
>>> the EAGAIN handling in the network drivers.
>>
>> I will try to push this branch sooner then since it affects more than just
>> TLS.  Part of the change includes a new flag we can use to assert that we
> Thanks John!
>> aren't just getting a stale rcvif (though there are also now assertions in
>> ip_output that should catch this case I think).
>>
> 
> 
> 
> Hi Andrey,
> 
> Yes, we were able to reproduce this issue in house. If you don't mind, I 
> prefer to wait for John's update - where he eliminates the EAGAIN 
> handling in the network drivers.

I have rebased the branch for this, but for now it will just panic sooner
I believe by tripping an assertion.  Can you grab the diff (or just the branch)
from the 'send_tags' branch at github/bsdjhb/freebsd and reproduce under a
kernel with INVARIANTS?  I think we will have to explicitly clear the 'rcvif'
pointer somewhere, but I want to see what the stack trace looks like so I can
think about the "right" place to clear it.

-- 
John Baldwin