sock_poll_wait: kill the no longer necessary barrier after poll_wait()

Now that poll_wait() provides a full barrier we can remove smp_mb() from
sock_poll_wait().

Also, the poll_does_not_wait() check before poll_wait() just adds the
unnecessary confusion, kill it. poll_wait() does the same "p && p->_qproc"
check.

Signed-off-by: Oleg Nesterov <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: oleg-nesterov

include/net/sock.h

@@ -2291,7 +2291,7 @@ static inline bool skwq_has_sleeper(struct socket_wq *wq)
 }
 
 /**
- * sock_poll_wait - place memory barrier behind the poll_wait call.
+ * sock_poll_wait - wrapper for the poll_wait call.
  * @filp:           file
  * @sock:           socket to wait on
  * @p:              poll_table
@@ -2301,15 +2301,12 @@ static inline bool skwq_has_sleeper(struct socket_wq *wq)
 static inline void sock_poll_wait(struct file *filp, struct socket *sock,
 				  poll_table *p)
 {
-	if (!poll_does_not_wait(p)) {
-		poll_wait(filp, &sock->wq.wait, p);
-		/* We need to be sure we are in sync with the
-		 * socket flags modification.
-		 *
-		 * This memory barrier is paired in the wq_has_sleeper.
-		 */
-		smp_mb();
-	}
+	/* Provides a barrier we need to be sure we are in sync
+	 * with the socket flags modification.
+	 *
+	 * This memory barrier is paired in the wq_has_sleeper.
+	 */
+	poll_wait(filp, &sock->wq.wait, p);
 }
 
 static inline void skb_set_hash_from_sk(struct sk_buff *skb, struct sock *sk)