netdev - Re: [Patch net-next] call sk_dst_reset when set SO

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Date:   Wed, 5 Dec 2018 16:13:32 -0800
From:   peng yu <yupeng0921@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [Patch net-next] call sk_dst_reset when set SO_DONTROUTE

The SO_DONTROUTE doesn't impact the TCP receiving path, but it should
block the ACK of the receiving packet. When there are too many packets
which are not ACKed, the client will stop to send packets, so the
sock.recv on the server side won't receive data after it received some
data. I extracted the test code from my customer's production
environment. The test code could reproduce the issue but it is not a
good example. I will rewrite a test code and re-submit the patch.On
Wed, Dec 5, 2018 at 3:17 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Wed, Dec 5, 2018 at 3:07 PM yupeng <yupeng0921@...il.com> wrote:
> >
> > after set SO_DONTROUTE to 1, the IP layer should not route packets if
> > the dest IP address is not in link scope. But if the socket has cached
> > the dst_entry, such packets would be routed until the sk_dst_cache
> > expires. So we should clean the sk_dst_cache when a user set
> > SO_DONTROUTE option. Below are server/client python scripts which
> > could reprodue this issue:
> >
> > server side code:
> > ==========================================================================
> > import socket
> > import struct
> >
> > s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
> > s.bind(('0.0.0.0', 9000))
> > s.listen(1)
> > sock, addr = s.accept()
> > sock.setsockopt(socket.SOL_SOCKET, socket.SO_DONTROUTE, struct.pack('i', 1))
> > while True:
> >     data = sock.recv(1024) # here the sock.recv should not return anything
>
> Why is that so ?
>
> What is the relation of input path with the SO_DONTROUTE which is for TX ?
>
> sk_dst_reset(sk) should not impact receive side ?
>
> Thanks for providing a test !
>
> >     print(data)
> > ==========================================================================
> >
> > client side code:
> > ==========================================================================
> > import socket
> > import time
> >
> > s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
> > s.connect(('server_address', 9000))
> > while True:
> >     s.send(b'foo')
> >     print('send foo')
> >     time.sleep(1)
> > ==========================================================================
> >
> > Signed-off-by: yupeng <yupeng0921@...il.com>
> > ---
> >  net/core/sock.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/net/core/sock.c b/net/core/sock.c
> > index f5bb89785e47..f00902c532cc 100644
> > --- a/net/core/sock.c
> > +++ b/net/core/sock.c
> > @@ -700,6 +700,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
> >                 break;
> >         case SO_DONTROUTE:
> >                 sock_valbool_flag(sk, SOCK_LOCALROUTE, valbool);
> > +               sk_dst_reset(sk);
> >                 break;
> >         case SO_BROADCAST:
> >                 sock_valbool_flag(sk, SOCK_BROADCAST, valbool);
> > --
> > 2.17.1
> >