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

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Message-ID: <c35f67d1-0190-cb64-74d9-54889eb1aef7@gmail.com>
Date:   Wed, 6 Feb 2019 16:28:25 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        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 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.

> 
> For the rds you mentioned, it doesn't wait for readers, this
> is why it needs to check against 0 and why it is different from
> this one.
> 
> Thanks.
>