linux-kernel - Re: [PATCH] net/mlx4_en: ensure rx_desc updating reaches HW before prod db updating

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Message-ID: <460fca68-f8a8-e3c4-2e60-e90dc0e2f843@oracle.com>
Date:   Mon, 22 Jan 2018 10:40:53 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     junxiao.bi@...cle.com, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [PATCH] net/mlx4_en: ensure rx_desc updating reaches HW before
 prod db updating

Hi Eric

On 01/22/2018 12:43 AM, Eric Dumazet wrote:
> On Sun, 2018-01-21 at 18:24 +0200, Tariq Toukan wrote:
>>
>> On 21/01/2018 11:31 AM, Tariq Toukan wrote:
>>>
>>>
>>> On 19/01/2018 5:49 PM, Eric Dumazet wrote:
>>>> On Fri, 2018-01-19 at 23:16 +0800, jianchao.wang wrote:
>>>>> Hi Tariq
>>>>>
>>>>> Very sad that the crash was reproduced again after applied the patch.
>>
>> Memory barriers vary for different Archs, can you please share more 
>> details regarding arch and repro steps?
> 
> Yeah, mlx4 NICs in Google fleet receive trillions of packets per
> second, and we never noticed an issue.
> 
> Although we are using a slightly different driver, using order-0 pages
> and fast pages recycling.
> 
> 
The driver we use will will set the page reference count to (size of pages)/stride, the
pages will be freed by networking stack when the reference become zero, and the order-3
pages maybe allocated soon, this give NIC device a chance to corrupt the pages which have
 been allocated by others, such as slab.
In the current version with order-0 and page recycling, maybe the corruption occurred on
the inbound packets sometimes and just cause some bad and invalid packets which will be
dropped.

Thanks
Jianchao