On 08/23/2016 12:03 PM, Eric Dumazet wrote:
On Tue, 2016-08-23 at 11:25 -0700, David Miller wrote:
From: Laura Abbott <labb...@redhat.com>
Date: Tue, 23 Aug 2016 10:53:26 -0700
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
end
Well, 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;
Fixes the test for me. You're welcome to take this as a Tested-by.
Thanks,
Laura