linux-kernel - [PATCH 09/11] net/tcp: tcp_splice_read: always do non-blocking reads

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Date:   Mon, 16 Oct 2023 22:35:56 +0200
From:   Ahelenia Ziemiańska 
        <nabijaczleweli@...ijaczleweli.xyz>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 09/11] net/tcp: tcp_splice_read: always do non-blocking reads

Otherwise we risk sleeping with the pipe locked for indeterminate
lengths of time.

sock_rcvtimeo() returns 0 if the second argument is true, so the
explicit re-try loop for empty read conditions can be removed
entirely.

Link: https://lore.kernel.org/linux-fsdevel/qk6hjuam54khlaikf2ssom6custxf5is2ekkaequf4hvode3ls@zgf7j5j4ubvw/t/#u
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@...ijaczleweli.xyz>
---
 net/ipv4/tcp.c | 30 +++---------------------------
 1 file changed, 3 insertions(+), 27 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3f66cdeef7de..09b562e2c1bf 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -782,7 +782,6 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
 		.len = len,
 		.flags = flags,
 	};
-	long timeo;
 	ssize_t spliced;
 	int ret;
 
@@ -797,7 +796,6 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
 
 	lock_sock(sk);
 
-	timeo = sock_rcvtimeo(sk, sock->file->f_flags & O_NONBLOCK);
 	while (tss.len) {
 		ret = __tcp_splice_read(sk, &tss);
 		if (ret < 0)
@@ -821,35 +819,13 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
 				ret = -ENOTCONN;
 				break;
 			}
-			if (!timeo) {
-				ret = -EAGAIN;
-				break;
-			}
-			/* if __tcp_splice_read() got nothing while we have
-			 * an skb in receive queue, we do not want to loop.
-			 * This might happen with URG data.
-			 */
-			if (!skb_queue_empty(&sk->sk_receive_queue))
-				break;
-			sk_wait_data(sk, &timeo, NULL);
-			if (signal_pending(current)) {
-				ret = sock_intr_errno(timeo);
-				break;
-			}
-			continue;
+			ret = -EAGAIN;
+			break;
 		}
 		tss.len -= ret;
 		spliced += ret;
 
-		if (!tss.len || !timeo)
-			break;
-		release_sock(sk);
-		lock_sock(sk);
-
-		if (sk->sk_err || sk->sk_state == TCP_CLOSE ||
-		    (sk->sk_shutdown & RCV_SHUTDOWN) ||
-		    signal_pending(current))
-			break;
+		break;
 	}
 
 	release_sock(sk);
-- 
2.39.2

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