netdev - Re: [PATCH bpf-next] bpf/devmap: convert remaining READ_ONCE() to rcu

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Message-ID: <20210628230545.GN4397@paulmck-ThinkPad-P17-Gen-1>
Date:   Mon, 28 Jun 2021 16:05:45 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Hangbin Liu <liuhangbin@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH bpf-next] bpf/devmap: convert remaining READ_ONCE() to
 rcu_dereference()

On Tue, Jun 29, 2021 at 01:00:51AM +0200, Toke Høiland-Jørgensen wrote:
> There were a couple of READ_ONCE()-invocations left-over by the devmap RCU
> conversion. Convert these to rcu_dereference() as well to avoid complaints
> from sparse.
> 
> Fixes: 782347b6bcad ("xdp: Add proper __rcu annotations to redirect map entries")
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>

Reviewed-by: Paul E. McKenney <paulmck@...nel.org>

> ---
>  kernel/bpf/devmap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index 2f6bd75cd682..7a0c008f751b 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -558,7 +558,7 @@ int dev_map_enqueue_multi(struct xdp_buff *xdp, struct net_device *dev_rx,
>  
>  	if (map->map_type == BPF_MAP_TYPE_DEVMAP) {
>  		for (i = 0; i < map->max_entries; i++) {
> -			dst = READ_ONCE(dtab->netdev_map[i]);
> +			dst = rcu_dereference(dtab->netdev_map[i]);
>  			if (!is_valid_dst(dst, xdp, exclude_ifindex))
>  				continue;
>  
> @@ -654,7 +654,7 @@ int dev_map_redirect_multi(struct net_device *dev, struct sk_buff *skb,
>  
>  	if (map->map_type == BPF_MAP_TYPE_DEVMAP) {
>  		for (i = 0; i < map->max_entries; i++) {
> -			dst = READ_ONCE(dtab->netdev_map[i]);
> +			dst = rcu_dereference(dtab->netdev_map[i]);
>  			if (!dst || dst->dev->ifindex == exclude_ifindex)
>  				continue;
>  
> -- 
> 2.32.0
>