tcp: switch back to proper tcp_skb_cb size check in tcp_init()

Revert to the tcp_skb_cb size check that tcp_init() had before commit
b4772ef879a8 ("net: use common macro for assering skb->cb[] available
size in protocol families"). As related commit 744d5a3e9fe2 ("net:
move skb->dropcount to skb->cb[]") explains, the
sock_skb_cb_check_size() mechanism was added to ensure that there is
space for dropcount, "for protocol families using it". But TCP is not
a protocol using dropcount, so tcp_init() doesn't need to provision
space for dropcount in the skb->cb[], and thus we can revert to the
older form of the tcp_skb_cb size check. Doing so allows TCP to use 4
more bytes of the skb->cb[] space.

Fixes: b4772ef879a8 ("net: use common macro for assering skb->cb[] available size in protocol families")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e79ed17..de02fb4 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3261,11 +3261,12 @@ static void __init tcp_init_mem(void)
 
 void __init tcp_init(void)
 {
-       unsigned long limit;
        int max_rshare, max_wshare, cnt;
+       unsigned long limit;
        unsigned int i;
 
-       sock_skb_cb_check_size(sizeof(struct tcp_skb_cb));
+       BUILD_BUG_ON(sizeof(struct tcp_skb_cb) >
+                    FIELD_SIZEOF(struct sk_buff, cb));
 
        percpu_counter_init(&tcp_sockets_allocated, 0, GFP_KERNEL);
        percpu_counter_init(&tcp_orphan_count, 0, GFP_KERNEL);