Re: [PATCH] netns: correctly use per-netns ipv4 sysctl_tcp_mem

On 07/09/2012 07:21 PM, David Miller wrote:

From: Huang Qiang <redacted>
Date: Mon, 9 Jul 2012 14:05:09 +0800

quoted

From: Yang Zhenzhang <redacted>

Now, kernel allows each net namespace to independently set up its levels
for tcp memory pressure thresholds.

But it seems there is a bug, as using the following steps:

[root@host socket]# lxc-start -n test -f config /bin/bash
[root@net-test socket]# ip route add default via 192.168.58.2
[root@net-test socket]# echo 0 0 0 > /proc/sys/net/ipv4/tcp_mem
[root@net-test socket]# scp root-Q0ErXNX1RuabR28l3DCWlg@public.gmane.org:/home/tcp_mem_test .

and it still can transport the "tcp_mem_test" file which we hope it
would not.

It's because inet_init() (net/ipv4/af_inet.c)initialize the
tcp_prot.sysctl_mem:
tcp_prot.sysctl_mem = init_net.ipv4.sysctl_tcp_mem;

So when the protocal is TCP, sk->sk_prot->sysctl_mem(following code)
always use the ipv4 sysctl_tcp_mem of init_net namespace rather than
it's own net namespace.
This patch simply set "prot" equal to net->ipv4.sysctl_tcp_mem when
the protocol type is TCP.

Signed-off-by: Yang Zhenzhang <redacted>

Another regression added by the socket memory cgroup code, BIG
SURPRISE.

Back from vacations: If I understand the submission correctly, this is
not a regression, since it seems to be only happening when those values
are set inside the network namespace - which was not possible before.

In any case, I believe from what I can see that the fix is already in
the way (haven't seen the whole backlog yet)