netsec: Remove rcu_read_lock() around XDP program invocation

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.
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Jassi Brar <jaswinder.singh@linaro.org>
Link: https://lore.kernel.org/bpf/20210624160609.292325-18-toke@redhat.com

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;
 }