netdev - Re: [PATCH net-next] net: core: Traverse the adjacency list from first entry

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Date:   Wed, 26 Oct 2016 09:05:35 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     idosch@...sch.org, davem@...emloft.net
Cc:     netdev@...r.kernel.org, mlxsw@...lanox.com,
        Ido Schimmel <idosch@...lanox.com>
Subject: Re: [PATCH net-next] net: core: Traverse the adjacency list from
 first entry

On 10/26/16 12:39 AM, idosch@...sch.org wrote:
> From: Ido Schimmel <idosch@...lanox.com>
> 
> netdev_next_lower_dev() returns NULL when we finished traversing the
> adjacency list ('iter' points to the list's head). Therefore, we must
> start traversing the list from the first entry and not its head.
> 
> Fixes: 1a3f060c1a47 ("net: Introduce new api for walking upper and lower devices")
> Signed-off-by: Ido Schimmel <idosch@...lanox.com>
> ---
>  net/core/dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index f55fb45..d9c937f 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5419,7 +5419,7 @@ int netdev_walk_all_lower_dev(struct net_device *dev,
>  	struct list_head *iter;
>  	int ret;
>  
> -	for (iter = &dev->adj_list.lower,
> +	for (iter = dev->adj_list.lower.next,
>  	     ldev = netdev_next_lower_dev(dev, &iter);
>  	     ldev;
>  	     ldev = netdev_next_lower_dev(dev, &iter)) {
> 

How about this instead? It keeps the 3 walk functions in sync modulo the rcu reference:


diff --git a/net/core/dev.c b/net/core/dev.c
index f55fb4536016..6aa43cd8cbb5 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5400,12 +5400,12 @@ static struct net_device *netdev_next_lower_dev(struct net_device *dev,
 {
	struct netdev_adjacent *lower;

-	lower = list_entry(*iter, struct netdev_adjacent, list);
+	lower = list_entry((*iter)->next, struct netdev_adjacent, list);

 	if (&lower->list == &dev->adj_list.lower)
 		return NULL;

-	*iter = lower->list.next;
+	*iter = &lower->list;

 	return lower->dev;
 }