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

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Date:   Wed, 6 Feb 2019 16:51:21 -0800
From:   Saeed Mahameed <saeedm@....mellanox.co.il>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        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.
>

I already suggested this, quoting myself from my first reply to this patch V0:
"another way to do it is not to do any refcounting in the irq handler
and fence cq removal via synchronize_irq(eq->irqn) on mlx5_eq_del_cq."

I already have a patch I was just waiting for Cong to push V2.