net-device: move xdp_prog to net_device_read_rx

xdp_prog is used in receive path, both from XDP enabled drivers
and from netif_elide_gro().

This patch also removes two 4-bytes holes.

Fixes: 43a71cd6 ("net-device: reorganize net_device fast path variables")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Coco Li <lixiaoyan@google.com>
Cc: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240102162220.750823-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/net_cachelines/net_device.rst

@@ -96,7 +96,7 @@ unsigned_char*                      dev_addr
 struct_netdev_queue*                _rx                     read_mostly         -                   netdev_get_rx_queue(rx)
 unsigned_int                        num_rx_queues                                                   
 unsigned_int                        real_num_rx_queues      -                   read_mostly         get_rps_cpu
-struct_bpf_prog*                    xdp_prog                                                        
+struct_bpf_prog*                    xdp_prog                -                   read_mostly         netif_elide_gro()
 unsigned_long                       gro_flush_timeout       -                   read_mostly         napi_complete_done
 int                                 napi_defer_hard_irqs    -                   read_mostly         napi_complete_done
 unsigned_int                        gro_max_size            -                   read_mostly         skb_gro_receive

include/linux/netdevice.h

@@ -2150,6 +2150,7 @@ struct net_device {
 
 	/* RX read-mostly hotpath */
 	__cacheline_group_begin(net_device_read_rx);
+	struct bpf_prog __rcu	*xdp_prog;
 	struct list_head	ptype_specific;
 	int			ifindex;
 	unsigned int		real_num_rx_queues;
@@ -2325,7 +2326,6 @@ struct net_device {
 	const unsigned char	*dev_addr;
 
 	unsigned int		num_rx_queues;
-	struct bpf_prog __rcu	*xdp_prog;
 #define GRO_LEGACY_MAX_SIZE	65536u
 /* TCP minimal MSS is 8 (TCP_MIN_GSO_SIZE),
  * and shinfo->gso_segs is a 16bit field.

net/core/dev.c

@@ -11670,7 +11670,7 @@ static void __init net_dev_struct_check(void)
 #ifdef CONFIG_NET_XGRESS
 	CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read_rx, tcx_ingress);
 #endif
-	CACHELINE_ASSERT_GROUP_SIZE(struct net_device, net_device_read_rx, 96);
+	CACHELINE_ASSERT_GROUP_SIZE(struct net_device, net_device_read_rx, 104);
 }
 
 /*