[Bug 1896734] Re: A privsep daemon spawned by neutron-openvswitch-agent hangs when debug logging is enabled (large number of registered NICs) - an RPC response is too large for msgpack
Dmitrii Shcherbakov
1896734 at bugs.launchpad.net
Thu Sep 24 19:51:31 UTC 2020
ip address show output on one of the affected nodes (for reference on
how large it is):
https://paste.ubuntu.com/p/cRf655Y8kt/
** Also affects: oslo.privsep
Importance: Undecided
Status: New
** Description changed:
+ When there is a large amount of netdevs registered in the kernel and
+ debug logging is enabled, neutron-openvswitch-agent and the privsep
+ daemon spawned by it hang since the RPC call result sent by the privsep
+ daemon over a unix socket exceeds the message sizes that the msgpack
+ library can handle.
+
+ The impact of this is that enabling debug logging on the cloud
+ completely stalls neutron-openvswitch-agents and makes them "dead" from
+ the Neutron server perspective.
+
+ The issue is summarized in detail in comment #5
+ https://bugs.launchpad.net/oslo.privsep/+bug/1896734/comments/5
+
+ ========================================================================
+ Old Description
+
While trying to debug a different issue, I encountered a situation where
privsep hangs in the process of handling a request from neutron-
openvswitch-agent when debug logging is enabled (juju debug-log neutron-
openvswitch=true):
https://bugs.launchpad.net/charm-neutron-openvswitch/+bug/1895652/comments/11
https://bugs.launchpad.net/charm-neutron-openvswitch/+bug/1895652/comments/12
The issue gets reproduced reliably in the environment where I
encountered it on all units. As a result, neutron-openvswitch-agent
services hang while waiting for a response from the privsep daemon and
do not progress past basic initialization. They never post any state
back to the Neutron server and thus are marked dead by it.
The processes though are shown as "active (running)" by systemd which
adds to the confusion since they do indeed start from the systemd's
perspective.
systemctl --no-pager status neutron-openvswitch-agent.service
● neutron-openvswitch-agent.service - Openstack Neutron Open vSwitch Plugin Agent
Loaded: loaded (/lib/systemd/system/neutron-openvswitch-agent.service; enabled; vendor preset: enabled)
Active: active (running) since Wed 2020-09-23 08:28:41 UTC; 25min ago
Main PID: 247772 (/usr/bin/python)
Tasks: 4 (limit: 9830)
CGroup: /system.slice/neutron-openvswitch-agent.service
├─247772 /usr/bin/python3 /usr/bin/neutron-openvswitch-agent --config-file=/etc/neutron/neutron.conf --config-file=/etc/neutron/plugins/ml2/openvswitch_…og
└─248272 /usr/bin/python3 /usr/bin/privsep-helper --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/ml2/openvswitch_agent.ini -…ck
--------------------------------------------------------
An strace shows that the privsep daemon tries to receive input from fd 3
which is the unix socket it uses to communicate with the client.
However, this is just one tread out of many spawned by the privsep
daemon so it is unlikely to be the root cause (there are 65 threads
there in total, see https://paste.ubuntu.com/p/fbGvN2P8rP/)
# there is one extra neutron-openvvswitch-agent running in a LXD container which can be ignored here (there is an octavia unit on the node which has a neutron-openvswitch subordinate)
root at node2:~# ps -eo pid,user,args --sort user | grep -P 'privsep.*openvswitch'
860690 100000 /usr/bin/python3 /usr/bin/privsep-helper --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/ml2/openvswitch_agent.ini --privsep_context neutron.privileged.default --privsep_sock_path /tmp/tmp910qakfk/privsep.sock
248272 root /usr/bin/python3 /usr/bin/privsep-helper --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/ml2/openvswitch_agent.ini --privsep_context neutron.privileged.default --privsep_sock_path /tmp/tmpcmwn7vom/privsep.sock
363905 root grep --color=auto -P privsep.*openvswitch
root at node2:~# strace -f -p 248453 2>&1
[pid 248786] futex(0x7f6a6401c1d0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 248475] futex(0x7f6a6c024590, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 248473] futex(0x7f6a746d9fd0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 248453] recvfrom(3,
root at node2:~# lsof -p 248453 | grep 3u
privsep-h 248453 root 3u unix 0xffff8e6d8abdec00 0t0 356522977 type=STREAM
root at node2:~# ss -pax | grep 356522977
u_str ESTAB 0 0 /tmp/tmp2afa3enn/privsep.sock 356522978
* 356522977 users:(("/usr/bin/python",pid=247567,fd=16))
u_str ESTAB 0 0 * 356522977
* 356522978 users:(("privsep-helper",pid=248453,fd=3))
root at node2:~# lsof -p 247567 | grep 16u
/usr/bin/ 247567 neutron 16u unix 0xffff8e6d8abdb400 0t0 356522978 /tmp/tmp2afa3enn/privsep.sock type=STREAM
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https://bugs.launchpad.net/bugs/1896734
Title:
A privsep daemon spawned by neutron-openvswitch-agent hangs when debug
logging is enabled (large number of registered NICs) - an RPC response
is too large for msgpack
Status in OpenStack neutron-openvswitch charm:
Invalid
Status in oslo.privsep:
New
Status in python-oslo.privsep package in Ubuntu:
New
Bug description:
When there is a large amount of netdevs registered in the kernel and
debug logging is enabled, neutron-openvswitch-agent and the privsep
daemon spawned by it hang since the RPC call result sent by the
privsep daemon over a unix socket exceeds the message sizes that the
msgpack library can handle.
The impact of this is that enabling debug logging on the cloud
completely stalls neutron-openvswitch-agents and makes them "dead"
from the Neutron server perspective.
The issue is summarized in detail in comment #5
https://bugs.launchpad.net/oslo.privsep/+bug/1896734/comments/5
========================================================================
Old Description
While trying to debug a different issue, I encountered a situation
where privsep hangs in the process of handling a request from neutron-
openvswitch-agent when debug logging is enabled (juju debug-log
neutron-openvswitch=true):
https://bugs.launchpad.net/charm-neutron-openvswitch/+bug/1895652/comments/11
https://bugs.launchpad.net/charm-neutron-openvswitch/+bug/1895652/comments/12
The issue gets reproduced reliably in the environment where I
encountered it on all units. As a result, neutron-openvswitch-agent
services hang while waiting for a response from the privsep daemon and
do not progress past basic initialization. They never post any state
back to the Neutron server and thus are marked dead by it.
The processes though are shown as "active (running)" by systemd which
adds to the confusion since they do indeed start from the systemd's
perspective.
systemctl --no-pager status neutron-openvswitch-agent.service
● neutron-openvswitch-agent.service - Openstack Neutron Open vSwitch Plugin Agent
Loaded: loaded (/lib/systemd/system/neutron-openvswitch-agent.service; enabled; vendor preset: enabled)
Active: active (running) since Wed 2020-09-23 08:28:41 UTC; 25min ago
Main PID: 247772 (/usr/bin/python)
Tasks: 4 (limit: 9830)
CGroup: /system.slice/neutron-openvswitch-agent.service
├─247772 /usr/bin/python3 /usr/bin/neutron-openvswitch-agent --config-file=/etc/neutron/neutron.conf --config-file=/etc/neutron/plugins/ml2/openvswitch_…og
└─248272 /usr/bin/python3 /usr/bin/privsep-helper --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/ml2/openvswitch_agent.ini -…ck
--------------------------------------------------------
An strace shows that the privsep daemon tries to receive input from fd
3 which is the unix socket it uses to communicate with the client.
However, this is just one tread out of many spawned by the privsep
daemon so it is unlikely to be the root cause (there are 65 threads
there in total, see https://paste.ubuntu.com/p/fbGvN2P8rP/)
# there is one extra neutron-openvvswitch-agent running in a LXD container which can be ignored here (there is an octavia unit on the node which has a neutron-openvswitch subordinate)
root at node2:~# ps -eo pid,user,args --sort user | grep -P 'privsep.*openvswitch'
860690 100000 /usr/bin/python3 /usr/bin/privsep-helper --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/ml2/openvswitch_agent.ini --privsep_context neutron.privileged.default --privsep_sock_path /tmp/tmp910qakfk/privsep.sock
248272 root /usr/bin/python3 /usr/bin/privsep-helper --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/ml2/openvswitch_agent.ini --privsep_context neutron.privileged.default --privsep_sock_path /tmp/tmpcmwn7vom/privsep.sock
363905 root grep --color=auto -P privsep.*openvswitch
root at node2:~# strace -f -p 248453 2>&1
[pid 248786] futex(0x7f6a6401c1d0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 248475] futex(0x7f6a6c024590, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 248473] futex(0x7f6a746d9fd0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 248453] recvfrom(3,
root at node2:~# lsof -p 248453 | grep 3u
privsep-h 248453 root 3u unix 0xffff8e6d8abdec00 0t0 356522977 type=STREAM
root at node2:~# ss -pax | grep 356522977
u_str ESTAB 0 0 /tmp/tmp2afa3enn/privsep.sock 356522978
* 356522977 users:(("/usr/bin/python",pid=247567,fd=16))
u_str ESTAB 0 0 * 356522977
* 356522978 users:(("privsep-helper",pid=248453,fd=3))
root at node2:~# lsof -p 247567 | grep 16u
/usr/bin/ 247567 neutron 16u unix 0xffff8e6d8abdb400 0t0 356522978 /tmp/tmp2afa3enn/privsep.sock type=STREAM
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