netdev - Re: [PATCH bpf-next 15/17] netsec: remove rcu_read

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Date:   Thu, 10 Jun 2021 08:30:25 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <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>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH bpf-next 15/17] netsec: remove rcu_read_lock() around XDP
 program invocation

On Wed, 9 Jun 2021 at 13:33, Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> The netsec driver has a rcu_read_lock()/rcu_read_unlock() pair around the
> full RX loop, covering everything up to and including xdp_do_flush(). This
> is actually the correct behaviour, but because it all happens in a single
> NAPI poll cycle (and thus under local_bh_disable()), it is also technically
> redundant.
>
> With the addition of RCU annotations to the XDP_REDIRECT map types that
> take bh execution into account, lockdep even understands this to be safe,
> so there's really no reason to keep the rcu_read_lock() around anymore, so
> let's just remove it.
>
> Cc: Jassi Brar <jaswinder.singh@...aro.org>
> Cc: Ilias Apalodimas <ilias.apalodimas@...aro.org>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  drivers/net/ethernet/socionext/netsec.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c
> index dfc85cc68173..20d148c019d8 100644
> --- a/drivers/net/ethernet/socionext/netsec.c
> +++ b/drivers/net/ethernet/socionext/netsec.c
> @@ -958,7 +958,6 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
>
>         xdp_init_buff(&xdp, PAGE_SIZE, &dring->xdp_rxq);
>
> -       rcu_read_lock();
>         xdp_prog = READ_ONCE(priv->xdp_prog);
>         dma_dir = page_pool_get_dma_dir(dring->page_pool);
>
> @@ -1069,8 +1068,6 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
>         }
>         netsec_finalize_xdp_rx(priv, xdp_act, xdp_xmit);
>
> -       rcu_read_unlock();
> -
>         return done;
>  }
>
> --
> 2.31.1
>

Acked-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>