netdev - [PATCH bpf-next v3 2/3] bpf: xdp, virtio_net use access ptr macro for xdp enable check

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Date:   Sun, 26 Jan 2020 16:14:01 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     bpf@...r.kernel.org
Cc:     bjorn.topel@...el.com, songliubraving@...com,
        john.fastabend@...il.com, ast@...nel.org, daniel@...earbox.net,
        toke@...hat.com, maciej.fijalkowski@...el.com,
        netdev@...r.kernel.org
Subject: [PATCH bpf-next v3 2/3] bpf: xdp, virtio_net use access ptr macro for xdp enable check

virtio_net currently relies on rcu critical section to access the xdp
program in its xdp_xmit handler. However, the pointer to the xdp program
is only used to do a NULL pointer comparison to determine if xdp is
enabled or not.

Use rcu_access_pointer() instead of rcu_dereference() to reflect this.
Then later when we drop rcu_read critical section virtio_net will not
need in special handling.

Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>
Signed-off-by: John Fastabend <john.fastabend@...il.com>
---
 drivers/net/virtio_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4d7d5434..945eabc 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -501,7 +501,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
 	/* Only allow ndo_xdp_xmit if XDP is loaded on dev, as this
 	 * indicate XDP resources have been successfully allocated.
 	 */
-	xdp_prog = rcu_dereference(rq->xdp_prog);
+	xdp_prog = rcu_access_pointer(rq->xdp_prog);
 	if (!xdp_prog)
 		return -ENXIO;
 
-- 
2.7.4