2018-10-03 15:08:55

by Yafang Shao

Subject: [PATCH net-next] inet: do not set backlog if listen fails

These two backlog members are not necessary set in inet_csk_listen_start().
Regarding sk_max_ack_backlog, it will be set in the caller inet_listen
and dccp_listen_start.
Regraing sk_ack_backlog, it is better to put it together with
sk_max_ack_backlog in the same function and only set on success.

Signed-off-by: Yafang Shao <[email protected]>
---
net/dccp/proto.c | 1 +
net/ipv4/af_inet.c | 1 +
net/ipv4/inet_connection_sock.c | 3 ---
3 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 875858c..34d48cd 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -959,6 +959,7 @@ int inet_dccp_listen(struct socket *sock, int backlog)
err = dccp_listen_start(sk, backlog);
if (err)
goto out;
+ sk->sk_ack_backlog = 0;
}
sk->sk_max_ack_backlog = backlog;
err = 0;
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 1fbe2f8..9690e0d 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -230,6 +230,7 @@ int inet_listen(struct socket *sock, int backlog)
if (err)
goto out;
tcp_call_bpf(sk, BPF_SOCK_OPS_TCP_LISTEN_CB, 0, NULL);
+ sk->sk_ack_backlog = 0;
}
sk->sk_max_ack_backlog = backlog;
err = 0;
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index dfd5009..c25d0b3 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -870,9 +870,6 @@ int inet_csk_listen_start(struct sock *sk, int backlog)
int err = -EADDRINUSE;

reqsk_queue_alloc(&icsk->icsk_accept_queue);
-
- sk->sk_max_ack_backlog = backlog;
- sk->sk_ack_backlog = 0;
inet_csk_delack_init(sk);

/* There is race window here: we announce ourselves listening,
--
1.8.3.1

2018-10-03 15:41:38

by Eric Dumazet

Subject: Re: [PATCH net-next] inet: do not set backlog if listen fails

On 10/03/2018 08:07 AM, Yafang Shao wrote:
> These two backlog members are not necessary set in inet_csk_listen_start().
> Regarding sk_max_ack_backlog, it will be set in the caller inet_listen
> and dccp_listen_start.
> Regraing sk_ack_backlog, it is better to put it together with
> sk_max_ack_backlog in the same function and only set on success.
>
> Signed-off-by: Yafang Shao <[email protected]>
> ---
> net/dccp/proto.c | 1 +
> net/ipv4/af_inet.c | 1 +
> net/ipv4/inet_connection_sock.c | 3 ---
> 3 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/net/dccp/proto.c b/net/dccp/proto.c
> index 875858c..34d48cd 100644
> --- a/net/dccp/proto.c
> +++ b/net/dccp/proto.c
> @@ -959,6 +959,7 @@ int inet_dccp_listen(struct socket *sock, int backlog)
> err = dccp_listen_start(sk, backlog);
> if (err)
> goto out;
> + sk->sk_ack_backlog = 0;


This is racy, remember that dccp and tcp have lockless listeners.

Do not change sk_ack_backlog after a TCP/DCCP socket is ready to accept new flows.

2018-10-05 01:55:19

by Yafang Shao

Subject: Re: [PATCH net-next] inet: do not set backlog if listen fails

On Wed, Oct 3, 2018 at 11:41 PM Eric Dumazet <[email protected]> wrote:
>
>
>
> On 10/03/2018 08:07 AM, Yafang Shao wrote:
> > These two backlog members are not necessary set in inet_csk_listen_start().
> > Regarding sk_max_ack_backlog, it will be set in the caller inet_listen
> > and dccp_listen_start.
> > Regraing sk_ack_backlog, it is better to put it together with
> > sk_max_ack_backlog in the same function and only set on success.
> >
> > Signed-off-by: Yafang Shao <[email protected]>
> > ---
> > net/dccp/proto.c | 1 +
> > net/ipv4/af_inet.c | 1 +
> > net/ipv4/inet_connection_sock.c | 3 ---
> > 3 files changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/net/dccp/proto.c b/net/dccp/proto.c
> > index 875858c..34d48cd 100644
> > --- a/net/dccp/proto.c
> > +++ b/net/dccp/proto.c
> > @@ -959,6 +959,7 @@ int inet_dccp_listen(struct socket *sock, int backlog)
> > err = dccp_listen_start(sk, backlog);
> > if (err)
> > goto out;
> > + sk->sk_ack_backlog = 0;
>
>
> This is racy, remember that dccp and tcp have lockless listeners.
>
> Do not change sk_ack_backlog after a TCP/DCCP socket is ready to accept new flows.

Understood. Thanks for your explanation.