linux-kernel - [PATCH 5.4 66/71] Revert "xsk: Do not sleep in poll() when need

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Date:   Mon, 20 Dec 2021 15:34:55 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH 5.4 66/71] Revert "xsk: Do not sleep in poll() when need_wakeup set"

From: Magnus Karlsson <magnus.karlsson@...el.com>

commit 0706a78f31c4217ca144f630063ec9561a21548d upstream.

This reverts commit bd0687c18e635b63233dc87f38058cd728802ab4.

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: bd0687c18e63 ("xsk: Do not sleep in poll() when need_wakeup set")
Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Link: https://lore.kernel.org/bpf/20211217145646.26449-1-magnus.karlsson@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/xdp/xsk.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -434,6 +434,8 @@ static __poll_t xsk_poll(struct file *fi
 	struct xdp_sock *xs = xdp_sk(sk);
 	struct xdp_umem *umem;
 
+	sock_poll_wait(file, sock, wait);
+
 	if (unlikely(!xsk_is_bound(xs)))
 		return mask;
 
@@ -445,8 +447,6 @@ static __poll_t xsk_poll(struct file *fi
 		else
 			/* Poll needs to drive Tx also in copy mode */
 			__xsk_sendmsg(sk);
-	} else {
-		sock_poll_wait(file, sock, wait);
 	}
 
 	if (xs->rx && !xskq_empty_desc(xs->rx))