tcp: preserve const qualifier in tcp_sk()

We can change tcp_sk() to propagate its argument const qualifier,
thanks to container_of_const().

We have two places where a const sock pointer has to be upgraded
to a write one. We have been using const qualifier for lockless
listeners to clearly identify points where writes could happen.

Add tcp_sk_rw() helper to better document these.

tcp_inbound_md5_hash(), __tcp_grow_window(), tcp_reset_check()
and tcp_rack_reo_wnd() get an additional const qualififer
for their @tp local variables.

smc_check_reset_syn_req() also needs a similar change.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 4 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index ca7f05a130d2..b4c08ac86983 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -472,10 +472,12 @@ enum tsq_flags {
 	TCPF_MTU_REDUCED_DEFERRED	= (1UL << TCP_MTU_REDUCED_DEFERRED),
 };
 
-static inline struct tcp_sock *tcp_sk(const struct sock *sk)
-{
-	return (struct tcp_sock *)sk;
-}
+#define tcp_sk(ptr) container_of_const(ptr, struct tcp_sock, inet_conn.icsk_inet.sk)
+
+/* Variant of tcp_sk() upgrading a const sock to a read/write tcp socket.
+ * Used in context of (lockless) tcp listeners.
+ */
+#define tcp_sk_rw(ptr) container_of(ptr, struct tcp_sock, inet_conn.icsk_inet.sk)
 
 struct tcp_timewait_sock {
 	struct inet_timewait_sock tw_sk;