netdev - Re: [net-next PATCH v4 01/16] net: qdisc: use rcu prefix and silence sparse warnings

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Date:	Wed, 10 Sep 2014 17:23:58 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	John Fastabend <john.fastabend@...il.com>
Cc:	xiyou.wangcong@...il.com, davem@...emloft.net, jhs@...atatu.com,
	netdev@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	brouer@...hat.com
Subject: Re: [net-next PATCH v4 01/16] net: qdisc: use rcu prefix and
 silence sparse warnings

On Wed, 2014-09-10 at 08:47 -0700, John Fastabend wrote:
> Add __rcu notation to qdisc handling by doing this we can make
> smatch output more legible. And anyways some of the cases should
> be using rcu_dereference() see qdisc_all_tx_empty(),
> qdisc_tx_chainging(), and so on.
> 
> Also *wake_queue() API is commonly called from driver timer routines
> without rcu lock or rtnl lock. So I added rcu_read_lock() blocks
> around netif_wake_subqueue and netif_tx_wake_queue.
> 
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>

...

>  
> @@ -416,10 +423,13 @@ static inline bool qdisc_all_tx_empty(const struct net_device *dev)
>  static inline bool qdisc_tx_changing(const struct net_device *dev)
>  {
>  	unsigned int i;
> +
>  	for (i = 0; i < dev->num_tx_queues; i++) {
>  		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
> -		if (txq->qdisc != txq->qdisc_sleeping)
> +		if (rcu_access_pointer(txq->qdisc) != txq->qdisc_sleeping) {
> +			rcu_read_unlock();

You forgot to remove this rcu_read_unlock();

>  			return true;
> +		}
>  	}
>  	return false;
>  }
> @@ -428,10 +438,13 @@ static inline bool qdisc_tx_changing(const struct net_device *dev)
>  static inline bool qdisc_tx_is_noop(const struct net_device *dev)
>  {
>  	unsigned int i;
> +
>  	for (i = 0; i < dev->num_tx_queues; i++) {
>  		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
> -		if (txq->qdisc != &noop_qdisc)
> +		if (rcu_dereference(txq->qdisc) != &noop_qdisc) {

		rcu_access_pointer()

> +			rcu_read_unlock();

You forgot to remove this rcu_read_unlock();

>  			return false;
> +		}
>  	}
>  	return true;
>  }



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