Re: [PATCH v1 net 1/4] neighbour: Add missing RCU annotation for neightbl_dump_info().

[Ido Schimmel <idosch@nvidia.com>]

On Mon, Sep 07, 2026 at 09:57:52PM +0000, Kuniyuki Iwashima wrote:
> neightbl_dump_info() fetches the first non-default neigh_parms
> with list_next_entry(&tbl->parms, ...) and iterates through the
> list with list_for_each_entry_from_rcu().
> 
> However, list_next_entry() does not use RCU helper.
> 
> Let's fetch the default parms with list_first_entry() and
> use list_for_each_entry_continue_rcu() for iteration.
> 
> Note that the first entry is always tbl->parms, which never goes
> away, so list_first_entry(&tbl->parms_list, ...) is safe.
> 
> Fixes: 4ae34be50064 ("neighbour: Convert RTM_GETNEIGHTBL to RCU.")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
> ---
>  net/core/neighbour.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 1349c0eedb64..4b17c2a15594 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -2611,8 +2611,9 @@ static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
>  			break;
>  
>  		nidx = 0;
> -		p = list_next_entry(&tbl->parms, list);
> -		list_for_each_entry_from_rcu(p, &tbl->parms_list, list) {
> +
> +		p = list_first_entry(&tbl->parms_list, struct neigh_parms, list);
> +		list_for_each_entry_continue_rcu(p, &tbl->parms_list, list) {
>  			if (!net_eq(neigh_parms_net(p), net))
>  				continue;

I find this more readable:

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 1349c0eedb64..3af539f5fd4b 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2611,11 +2611,13 @@ static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 			break;
 
 		nidx = 0;
-		p = list_next_entry(&tbl->parms, list);
-		list_for_each_entry_from_rcu(p, &tbl->parms_list, list) {
+		list_for_each_entry_rcu(p, &tbl->parms_list, list) {
 			if (!net_eq(neigh_parms_net(p), net))
 				continue;
 
+			if (!p->dev)
+				continue;
+
 			if (nidx < neigh_skip)
 				goto next;
 
Then patch #3 becomes:

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 3af539f5fd4b..b4d8e5b6832c 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2615,7 +2615,7 @@ static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 			if (!net_eq(neigh_parms_net(p), net))
 				continue;
 
-			if (!p->dev)
+			if (!p->dev || p->dev == blackhole_netdev)
 				continue;
 
 			if (nidx < neigh_skip)