netdev - [PATCH net] Revert "xsk: Do not sleep in poll() when need

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Date:   Tue,  4 Jan 2022 17:57:01 +0800
From:   Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To:     netdev@...r.kernel.org
Cc:     Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        bpf@...r.kernel.org
Subject: [PATCH net] Revert "xsk: Do not sleep in poll() when need_wakeup set"

This reverts commit bd0687c18e635b63233dc87f38058cd728802ab4.

When working with epoll, if the application encounters tx full, the
application will enter epoll_wait and wait for tx to be awakened when
there is room.

In the current situation, when tx is full pool->cached_need_wakeup may
not be 0 (regardless of whether the driver supports wakeup, or whether
the user uses XDP_USE_NEED_WAKEUP). The result is that if the user
enters epoll_wait, because soock_poll_wait is not called, causing the
user process to not be awakened.

Fixes: bd0687c18e63 ("xsk: Do not sleep in poll() when need_wakeup set")
Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
---
 net/xdp/xsk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index e3d35850fdea..28ef3f4465ae 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -677,6 +677,8 @@ 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;
 
@@ -688,8 +690,6 @@ 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))
-- 
2.31.0