linux-kernel - Re: [net-next PATCH 1/2] macvtap: slient sparse warnings

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Message-ID: <1371102507.3252.96.camel@edumazet-glaptop>
Date:	Wed, 12 Jun 2013 22:48:27 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [net-next PATCH 1/2] macvtap: slient sparse warnings

On Thu, 2013-06-13 at 12:21 +0800, Jason Wang wrote:
> This patch silents the following sparse warnings:
> 
> dr
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/net/macvtap.c      |    2 +-
>  include/linux/if_macvlan.h |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 992151c..acf55ba 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -429,7 +429,7 @@ static int macvtap_open(struct inode *inode, struct file *file)
>  	if (!q)
>  		goto out;
>  
> -	q->sock.wq = &q->wq;
> +	rcu_assign_pointer(q->sock.wq, &q->wq);

Since nobody but you [1] can access this object at that time, you could
rather use
	RCU_INIT_POINTER(q->sock.wq, &q->wq);

rcu_assign_pointer() is also a documentation point (memory barrier)

By using RCU_INIT_POINTER() you clearly show that you know you need no
memory barrier.

>  	init_waitqueue_head(&q->wq.wait);

[1] :
or else, this init_waitqueue_head() should be done _before_ the
rcu_asign_pointer()

>  	q->sock.type = SOCK_RAW;
>  	q->sock.state = SS_CONNECTED;


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