xdp: Fix xsk_generic_xmit errno

stable inclusion
from linux-4.19.130
commit d10a69cadbf73f07cb555c260026d3ec9bf921b3

--------------------------------

[ Upstream commit aa2cad06 ]

Propagate sock_alloc_send_skb error code, not set it to
EAGAIN unconditionally, when fail to allocate skb, which
might cause that user space unnecessary loops.

Fixes: 35fcde7f ("xsk: support for Tx")
Signed-off-by: NLi RongQing <lirongqing@baidu.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NBjörn Töpel <bjorn.topel@intel.com>
Link: https://lore.kernel.org/bpf/1591852266-24017-1-git-send-email-lirongqing@baidu.comSigned-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NLi Aichun <liaichun@huawei.com>
Reviewed-by: Nguodeqing <geffrey.guo@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

net/xdp/xsk.c

@@ -233,10 +233,8 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
 
 		len = desc.len;
 		skb = sock_alloc_send_skb(sk, len, 1, &err);
-		if (unlikely(!skb)) {
-			err = -EAGAIN;
+		if (unlikely(!skb))
 			goto out;
-		}
 
 		skb_put(skb, len);
 		addr = desc.addr;