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

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Message-ID: <af562737-4a3e-0429-1fd6-fc25c3e3f867@mellanox.com>
Date:   Sun, 14 Jan 2018 11:47:13 +0200
From:   Tariq Toukan <tariqt@...lanox.com>
To:     "jianchao.wang" <jianchao.w.wang@...cle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     tariqt@...lanox.com, 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

Thanks Jianchao for your patch.

And Thank you guys for your reviews, much appreciated.
I was off-work on Friday and Saturday.

On 14/01/2018 4:40 AM, jianchao.wang wrote:
> Dear all
> 
> Thanks for the kindly response and reviewing. That's really appreciated.
> 
> On 01/13/2018 12:46 AM, Eric Dumazet wrote:
>>> Does this need to be dma_wmb(), and should it be in
>>> mlx4_en_update_rx_prod_db ?
>>>
>> +1 on dma_wmb()
>>
>> On what architecture bug was observed ?
> This issue was observed on x86-64.
> And I will send a new patch, in which replace wmb() with dma_wmb(), to customer
> to confirm.

+1 on dma_wmb, let us know once customer confirms.
Please place it within mlx4_en_update_rx_prod_db as suggested.
All other calls to mlx4_en_update_rx_prod_db are in control/slow path so 
I prefer being on the safe side, and care less about bulking the barrier.

Thanks,
Tariq