* [REGRESSION] Select hang with zero sized UDP packets
@ 2016-08-23 17:53 Laura Abbott
2016-08-23 18:25 ` David Miller
0 siblings, 1 reply; 12+ messages in thread
From: Laura Abbott @ 2016-08-23 17:53 UTC (permalink / raw)
To: David S. Miller, Alexey Kuznetsov, James Morris,
Hideaki YOSHIFUJI, Patrick McHardy, Sam Kumar, Willem de Bruijn
Cc: netdev, Linux Kernel Mailing List
Hi,
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
which roughly corresponds to this in C
int main()
{
int fd1, fd2;
struct sockaddr_in addr1;
unsigned int len1;
int ret;
fd_set rfds;
fd1 = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_UDP);
fd2 = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_UDP);
if (fd1 < 0 || fd2 < 0) {
printf("socket fail");
exit(1);
}
len1 = sizeof(addr1);
memset(&addr1, 0, sizeof(addr1));
addr1.sin_family = AF_INET;
addr1.sin_addr.s_addr = inet_addr("127.0.0.1");
addr1.sin_port = htons(0);
ret = bind(fd1, (struct sockaddr *)&addr1, len1);
if (ret < 0) {
printf("fu %d\n", errno);
exit(1);
}
ret = getsockname(fd1, (struct sockaddr *)&addr1, &len1);
if (ret < 0) {
printf("getsockname failed %d\n", errno);
exit(1);
}
ret = sendto(fd2, "", 0, 0, (struct sockaddr *)&addr1, len1);
if (ret < 0) {
printf("sendto failed %d\n", errno);
exit(1);
}
FD_ZERO(&rfds);
FD_SET(fd1, &rfds);
// hang here
select(fd1+1, &rfds, NULL, NULL, NULL);
}
Bisection showed
commit e6afc8ace6dd5cef5e812f26c72579da8806f5ac
Author: samanthakumar <samanthakumar@google.com>
Date: Tue Apr 5 12:41:15 2016 -0400
udp: remove headers from UDP packets before queueing
Remove UDP transport headers before queueing packets for reception.
This change simplifies a follow-up patch to add MSG_PEEK support.
Signed-off-by: Sam Kumar <samanthakumar@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
As the offending commit. The issue is still reproducible on master
as of this morning and I don't see anything explicitly tagged in
net-next as fixing this.
Any ideas?
Thanks,
Laura
[1] https://bugzilla.redhat.com/show_bug.cgi?id=1365940
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [REGRESSION] Select hang with zero sized UDP packets
2016-08-23 17:53 [REGRESSION] Select hang with zero sized UDP packets Laura Abbott
@ 2016-08-23 18:25 ` David Miller
2016-08-23 19:03 ` Eric Dumazet
2016-08-24 8:22 ` [REGRESSION] Select hang with zero sized UDP packets Dan Akunis
0 siblings, 2 replies; 12+ messages in thread
From: David Miller @ 2016-08-23 18:25 UTC (permalink / raw)
To: labbott
Cc: kuznet, jmorris, yoshfuji, kaber, samanthakumar, willemb, netdev,
linux-kernel
From: Laura Abbott <labbott@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.
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [REGRESSION] Select hang with zero sized UDP packets
2016-08-23 18:25 ` David Miller
@ 2016-08-23 19:03 ` Eric Dumazet
2016-08-23 20:06 ` Laura Abbott
2016-08-24 8:22 ` [REGRESSION] Select hang with zero sized UDP packets Dan Akunis
1 sibling, 1 reply; 12+ messages in thread
From: Eric Dumazet @ 2016-08-23 19:03 UTC (permalink / raw)
To: David Miller
Cc: labbott, kuznet, jmorris, yoshfuji, kaber, samanthakumar,
willemb, netdev, linux-kernel
On Tue, 2016-08-23 at 11:25 -0700, David Miller wrote:
> From: Laura Abbott <labbott@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;
^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [REGRESSION] Select hang with zero sized UDP packets
2016-08-23 19:03 ` Eric Dumazet
@ 2016-08-23 20:06 ` Laura Abbott
2016-08-23 20:42 ` Eric Dumazet
2016-08-23 20:53 ` [PATCH net] udp: fix poll() issue with zero sized packets Eric Dumazet
0 siblings, 2 replies; 12+ messages in thread
From: Laura Abbott @ 2016-08-23 20:06 UTC (permalink / raw)
To: Eric Dumazet, David Miller
Cc: kuznet, jmorris, yoshfuji, kaber, samanthakumar, willemb, netdev,
linux-kernel
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 <labbott@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
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [REGRESSION] Select hang with zero sized UDP packets
2016-08-23 20:06 ` Laura Abbott
@ 2016-08-23 20:42 ` Eric Dumazet
2016-08-23 20:53 ` [PATCH net] udp: fix poll() issue with zero sized packets Eric Dumazet
1 sibling, 0 replies; 12+ messages in thread
From: Eric Dumazet @ 2016-08-23 20:42 UTC (permalink / raw)
To: Laura Abbott
Cc: David Miller, kuznet, jmorris, yoshfuji, kaber, samanthakumar,
willemb, netdev, linux-kernel
On Tue, 2016-08-23 at 13:06 -0700, Laura Abbott wrote:
>
> Fixes the test for me. You're welcome to take this as a Tested-by.
Thanks Laura, I will submit an official patch immediately.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [PATCH net] udp: fix poll() issue with zero sized packets
2016-08-23 20:06 ` Laura Abbott
2016-08-23 20:42 ` Eric Dumazet
@ 2016-08-23 20:53 ` Eric Dumazet
2016-08-23 20:56 ` Eric Dumazet
2016-08-23 20:59 ` [PATCH v2 " Eric Dumazet
1 sibling, 2 replies; 12+ messages in thread
From: Eric Dumazet @ 2016-08-23 20:53 UTC (permalink / raw)
To: Laura Abbott; +Cc: David Miller, samanthakumar, willemb, netdev
From: Eric Dumazet <edumazet@google.com>
Laura tracked poll() [and friends] regression caused by commit
e6afc8ace6dd ("udp: remove headers from UDP packets before queueing")
udp_poll() needs to know if there is a valid packet in receive queue,
even if its payload length is 0.
Change first_packet_length() to return an signed int, and use -1
as the indication of an empty queue.
Fixes: e6afc8ace6dd ("udp: remove headers from UDP packets before queueing")
Reported-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Laura Abbott <labbott@redhat.com>
---
net/ipv4/udp.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index e61f7cd65d08..2a2ac9e0c985 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_t(int, 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;
^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH net] udp: fix poll() issue with zero sized packets
2016-08-23 20:53 ` [PATCH net] udp: fix poll() issue with zero sized packets Eric Dumazet
@ 2016-08-23 20:56 ` Eric Dumazet
2016-08-23 20:59 ` [PATCH v2 " Eric Dumazet
1 sibling, 0 replies; 12+ messages in thread
From: Eric Dumazet @ 2016-08-23 20:56 UTC (permalink / raw)
To: Laura Abbott; +Cc: David Miller, samanthakumar, willemb, netdev
On Tue, 2016-08-23 at 13:53 -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
>
...
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index e61f7cd65d08..2a2ac9e0c985 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)
I'll send a V2, updating the comment to :
Returns the length of found skb, or -1 if none is found.
(Thanks Willem for noticing this)
^ permalink raw reply [flat|nested] 12+ messages in thread
* [PATCH v2 net] udp: fix poll() issue with zero sized packets
2016-08-23 20:53 ` [PATCH net] udp: fix poll() issue with zero sized packets Eric Dumazet
2016-08-23 20:56 ` Eric Dumazet
@ 2016-08-23 20:59 ` Eric Dumazet
2016-08-23 23:39 ` David Miller
1 sibling, 1 reply; 12+ messages in thread
From: Eric Dumazet @ 2016-08-23 20:59 UTC (permalink / raw)
To: Laura Abbott; +Cc: David Miller, samanthakumar, willemb, netdev
From: Eric Dumazet <edumazet@google.com>
Laura tracked poll() [and friends] regression caused by commit
e6afc8ace6dd ("udp: remove headers from UDP packets before queueing")
udp_poll() needs to know if there is a valid packet in receive queue,
even if its payload length is 0.
Change first_packet_length() to return an signed int, and use -1
as the indication of an empty queue.
Fixes: e6afc8ace6dd ("udp: remove headers from UDP packets before queueing")
Reported-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Laura Abbott <labbott@redhat.com>
---
v2: fix the comment/doc (Willem)
net/ipv4/udp.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index e61f7cd65d08..00d18c57c83c 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1182,13 +1182,13 @@ out:
* @sk: socket
*
* Drops all bad checksum frames, until a valid one is found.
- * Returns the length of found skb, or 0 if none is found.
+ * Returns the length of found skb, or -1 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_t(int, 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;
^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH v2 net] udp: fix poll() issue with zero sized packets
2016-08-23 20:59 ` [PATCH v2 " Eric Dumazet
@ 2016-08-23 23:39 ` David Miller
0 siblings, 0 replies; 12+ messages in thread
From: David Miller @ 2016-08-23 23:39 UTC (permalink / raw)
To: eric.dumazet; +Cc: labbott, samanthakumar, willemb, netdev
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 23 Aug 2016 13:59:33 -0700
> From: Eric Dumazet <edumazet@google.com>
>
> Laura tracked poll() [and friends] regression caused by commit
> e6afc8ace6dd ("udp: remove headers from UDP packets before queueing")
>
> udp_poll() needs to know if there is a valid packet in receive queue,
> even if its payload length is 0.
>
> Change first_packet_length() to return an signed int, and use -1
> as the indication of an empty queue.
>
> Fixes: e6afc8ace6dd ("udp: remove headers from UDP packets before queueing")
> Reported-by: Laura Abbott <labbott@redhat.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Tested-by: Laura Abbott <labbott@redhat.com>
> ---
> v2: fix the comment/doc (Willem)
Applied and queued up for -stable, thanks.
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [REGRESSION] Select hang with zero sized UDP packets
2016-08-23 18:25 ` David Miller
2016-08-23 19:03 ` Eric Dumazet
@ 2016-08-24 8:22 ` Dan Akunis
2016-08-24 13:02 ` Eric Dumazet
2016-08-24 13:42 ` One Thousand Gnomes
1 sibling, 2 replies; 12+ messages in thread
From: Dan Akunis @ 2016-08-24 8:22 UTC (permalink / raw)
To: labbott, David Miller
Cc: kuznet, jmorris, yoshfuji, kaber, samanthakumar, willemb, netdev,
linux-kernel
When select wakes up on a UDP socket, user is expecting to get data. Getting
0 from recvfrom() or whatever read function she uses, is a wrong attitude.
I agree with David.
The unit test that expects select to wake up is wrong and should be changed.
-----Original Message-----
From: David Miller
Sent: Tuesday, August 23, 2016 9:25 PM
To: labbott@redhat.com
Cc: kuznet@ms2.inr.ac.ru ; jmorris@namei.org ; yoshfuji@linux-ipv6.org ;
kaber@trash.net ; samanthakumar@google.com ; willemb@google.com ;
netdev@vger.kernel.org ; linux-kernel@vger.kernel.org
Subject: Re: [REGRESSION] Select hang with zero sized UDP packets
From: Laura Abbott <labbott@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.
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [REGRESSION] Select hang with zero sized UDP packets
2016-08-24 8:22 ` [REGRESSION] Select hang with zero sized UDP packets Dan Akunis
@ 2016-08-24 13:02 ` Eric Dumazet
2016-08-24 13:42 ` One Thousand Gnomes
1 sibling, 0 replies; 12+ messages in thread
From: Eric Dumazet @ 2016-08-24 13:02 UTC (permalink / raw)
To: Dan Akunis
Cc: labbott, David Miller, kuznet, jmorris, yoshfuji, kaber,
samanthakumar, willemb, netdev, linux-kernel
On Wed, 2016-08-24 at 11:22 +0300, Dan Akunis wrote:
> When select wakes up on a UDP socket, user is expecting to get data. Getting
> 0 from recvfrom() or whatever read function she uses, is a wrong attitude.
> I agree with David.
>
> The unit test that expects select to wake up is wrong and should be changed.
>
Please do not top post on netdev mailing list.
Program is fine and wont be changed to work around a kernel bug.
We definitely can send and receive UDP messages with 0 payload.
So select() should unblock when one such frame is received, otherwise
you could fill up the receive queue with a lot of frames like that and
when SO_RCVBUF limit is reached, block future messages.
UDP is a datagram protocol.
Bug fix is merged :
https://git.kernel.org/cgit/linux/kernel/git/davem/net.git/commit/?id=e83c6744e81abc93a20d0eb3b7f504a176a6126a
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [REGRESSION] Select hang with zero sized UDP packets
2016-08-24 8:22 ` [REGRESSION] Select hang with zero sized UDP packets Dan Akunis
2016-08-24 13:02 ` Eric Dumazet
@ 2016-08-24 13:42 ` One Thousand Gnomes
1 sibling, 0 replies; 12+ messages in thread
From: One Thousand Gnomes @ 2016-08-24 13:42 UTC (permalink / raw)
To: Dan Akunis
Cc: labbott, David Miller, kuznet, jmorris, yoshfuji, kaber,
samanthakumar, willemb, netdev, linux-kernel
On Wed, 24 Aug 2016 11:22:09 +0300
"Dan Akunis" <dan.akunis@gmail.com> wrote:
> When select wakes up on a UDP socket, user is expecting to get data. Getting
> 0 from recvfrom() or whatever read function she uses, is a wrong attitude.
> I agree with David.
>
> The unit test that expects select to wake up is wrong and should be changed.
The unit test is correct.
The behaviour of a 0 byte frame is actually well established and a 0 byte
data frame is a meaningful message is several protocols. It is distinct
from no pending data because that would report EWOULDBLOCK. It's more fun
with regard to EOF but UDP has no EOF semantics. If you want to
understand how to handle zero length datagrams in a connection oriented
protocol the old DECnet documentation covers it in all its pain 8)
Alan
^ permalink raw reply [flat|nested] 12+ messages in thread
end of thread, other threads:[~2016-08-24 13:43 UTC | newest]
Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-08-23 17:53 [REGRESSION] Select hang with zero sized UDP packets Laura Abbott
2016-08-23 18:25 ` David Miller
2016-08-23 19:03 ` Eric Dumazet
2016-08-23 20:06 ` Laura Abbott
2016-08-23 20:42 ` Eric Dumazet
2016-08-23 20:53 ` [PATCH net] udp: fix poll() issue with zero sized packets Eric Dumazet
2016-08-23 20:56 ` Eric Dumazet
2016-08-23 20:59 ` [PATCH v2 " Eric Dumazet
2016-08-23 23:39 ` David Miller
2016-08-24 8:22 ` [REGRESSION] Select hang with zero sized UDP packets Dan Akunis
2016-08-24 13:02 ` Eric Dumazet
2016-08-24 13:42 ` One Thousand Gnomes
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