Re: [REGRESSION] Select hang with zero sized UDP packets
From: Eric Dumazet <hidden>
Date: 2016-08-23 19:04:12
Also in:
lkml
Subsystem:
networking [general], the rest, user datagram protocol (udp) · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Willem de Bruijn
On Tue, 2016-08-23 at 11:25 -0700, David Miller wrote:
From: Laura Abbott <redacted> Date: Tue, 23 Aug 2016 10:53:26 -0700quoted
Fedora received a report[1] of a unit test failing on Ruby when using the 4.7 kernel. This was a test to send a zero sized UDP packet. With the 4.7 kernel, the test now timing out on a select instead of completing. The reduced ruby test is def test_udp_recvfrom_nonblock u1 = UDPSocket.new u2 = UDPSocket.new u1.bind("127.0.0.1", 0) u2.send("", 0, u1.getsockname) IO.select [u1] # test gets stuck here ensure u1.close if u1 u2.close if u2 endWell, if there is no data, should select really wake up? I think it's valid not to.
There are skb in receive queue, with skb->len = 0 This looks like a bug in first_packet_length() or poll logic. Definitely something we can fix. Maybe with :
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index e61f7cd65d08..380c05a84041 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c@@ -1184,11 +1184,11 @@ out: * Drops all bad checksum frames, until a valid one is found. * Returns the length of found skb, or 0 if none is found. */ -static unsigned int first_packet_length(struct sock *sk) +static int first_packet_length(struct sock *sk) { struct sk_buff_head list_kill, *rcvq = &sk->sk_receive_queue; struct sk_buff *skb; - unsigned int res; + int res; __skb_queue_head_init(&list_kill);
@@ -1203,7 +1203,7 @@ static unsigned int first_packet_length(struct sock *sk) __skb_unlink(skb, rcvq); __skb_queue_tail(&list_kill, skb); } - res = skb ? skb->len : 0; + res = skb ? skb->len : -1; spin_unlock_bh(&rcvq->lock); if (!skb_queue_empty(&list_kill)) {
@@ -1232,7 +1232,7 @@ int udp_ioctl(struct sock *sk, int cmd, unsigned long arg) case SIOCINQ: { - unsigned int amount = first_packet_length(sk); + int amount = max(0, first_packet_length(sk)); return put_user(amount, (int __user *)arg); }
@@ -2184,7 +2184,7 @@ unsigned int udp_poll(struct file *file, struct socket *sock, poll_table *wait) /* Check for false positives due to checksum errors */ if ((mask & POLLRDNORM) && !(file->f_flags & O_NONBLOCK) && - !(sk->sk_shutdown & RCV_SHUTDOWN) && !first_packet_length(sk)) + !(sk->sk_shutdown & RCV_SHUTDOWN) && first_packet_length(sk) == -1) mask &= ~(POLLIN | POLLRDNORM); return mask;