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

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Message-ID: <1515792119.131759.52.camel@gmail.com>
Date:   Fri, 12 Jan 2018 13:21:59 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jianchao Wang <jianchao.w.wang@...cle.com>
Cc:     tariqt@...lanox.com, junxiao.bi@...cle.com, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/mlx4_en: ensure rx_desc updating reaches HW before
 prod db updating

On Fri, 2018-01-12 at 13:01 -0800, Saeed Mahameed wrote:

> which is better to grasp ?:
> 
> update_doorbell() {
>     dma_wmb();
>     ring->db = prod;
> }

This one is IMO the most secure one (least surprise)

Considering the time it took to discover this bug, I would really play
safe.

But obviously I do not maintain mlx4.