netdev - Re: help on iproute2 hangs

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Date:   Thu, 1 Mar 2018 11:36:47 -0700
From:   David Ahern <dsahern@...il.com>
To:     William Tu <u9012063@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Cc:     chrism@...lanox.com
Subject: Re: help on iproute2 hangs

On 3/1/18 10:29 AM, William Tu wrote:
> Hi,
> 
> We're running commands below on kernel 4.15.0:
> 1) ip netns add at_ns0
> 2) ip link add p0 type veth peer name ovs-p0
> 3) ip link set p0 netns at_ns0
> 4) ip link set dev ovs-p0 up

# uname -a
Linux kenny-jessie3 4.16.0-rc2+ #162 SMP Thu Mar 1 08:48:58 PST 2018
x86_64 GNU/Linux

# bash -x /tmp/2
+ ip netns add at_ns0
+ ip link add p0 type veth peer name ovs-p0
+ ip link set p0 netns at_ns0
+ ip link set dev ovs-p0 up

Works fine for me on top of tree.

What is the output of 'cat /proc/<pid>/stack' when it hangs?


> 
> However, it always hangs at creating veth peer, command (2) when we
> run above commands in GNU autotest. Running the same commands in a
> bash script works fine.
> 
> Running bisect on iproute2, the first bad commit is
> commit 72a2ff3916e59d2132a7d613d9e8f5eb372ba43e
> Author: Chris Mi <chrism@...lanox.com>
> Date:   Fri Jan 12 14:13:15 2018 +0900
> 
>    lib/libnetlink: Add a new function rtnl_talk_iov
> 
>    rtnl_talk can only send a single message to kernel. Add a new function
>    rtnl_talk_iov that can send multiple messages to kernel.
>    rtnl_talk_iov takes struct iovec * and iovlen as arguments.
> 
> GDB shows it hangs on
> #0  0x00007f9c92e6b330 in recvmsg () from /lib/x86_64-linux-gnu/libc.so.6
> #1  0x000000000044eac6 in __rtnl_recvmsg ()
> #2  0x000000000044eb95 in rtnl_recvmsg ()
> #3  0x000000000044ed46 in __rtnl_talk_iov ()
> #4  0x000000000044fbb8 in rtnl_talk ()
> #5  0x0000000000422554 in iplink_modify ()
> 
> Any suggestion about how to debug this?
> Thanks
> William
>