Revert "xsk: Do not sleep in poll() when need_wakeup set"

commit 0706a78 upstream.

This reverts commit bd0687c.

This patch causes a Tx only workload to go to sleep even when it does
not have to, leading to misserable performance in skb mode. It fixed
one rare problem but created a much worse one, so this need to be
reverted while I try to craft a proper solution to the original
problem.

Fixes: bd0687c ("xsk: Do not sleep in poll() when need_wakeup set")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211217145646.26449-1-magnus.karlsson@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/xdp/xsk.c

@@ -499,6 +499,8 @@ static __poll_t xsk_poll(struct file *file, struct socket *sock,
 	struct xdp_sock *xs = xdp_sk(sk);
 	struct xsk_buff_pool *pool;
 
+	sock_poll_wait(file, sock, wait);
+
 	if (unlikely(!xsk_is_bound(xs)))
 		return mask;
 
@@ -510,8 +512,6 @@ static __poll_t xsk_poll(struct file *file, struct socket *sock,
 		else
 			/* Poll needs to drive Tx also in copy mode */
 			__xsk_sendmsg(sk);
-	} else {
-		sock_poll_wait(file, sock, wait);
 	}
 
 	if (xs->rx && !xskq_prod_is_empty(xs->rx))