netdev - Re: [Patch net-next v2] mlx5: use RCU lock in mlx5_eq_cq

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Message-ID: <CAM_iQpVF-71uQtybZLqLDWZQS=JxjD_23fAjxyfy7oLBzw-BoA@mail.gmail.com>
Date:   Wed, 6 Feb 2019 16:53:15 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [Patch net-next v2] mlx5: use RCU lock in mlx5_eq_cq_get()

On Wed, Feb 6, 2019 at 4:28 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
>
> On 02/06/2019 04:04 PM, Cong Wang wrote:
>
> > synchronize_irq() is called before mlx5_cq_put(), so I don't
> > see why readers could get 0 refcnt.
>
> Then the more reasons to get rid of the refcount increment/decrement completely ...
>
> Technically, even the rcu_read_lock() and rcu_read_unlock() are not needed,
> since synchronize_irq() is enough.

Excellent point.

For the refcnt, I am afraid we still have to hold refcnt for the tasklet,
mlx5_cq_tasklet_cb. But yeah, should be safe to remove from IRQ
path.