Bug 1446184

Summary: dockerd hangs if a EventMemberJoin is received while joining a Node found in KV store
Product: Red Hat Enterprise Linux 7 Reporter: Sergio Lopez <slopezpa>
Component: dockerAssignee: Antonio Murdaca <amurdaca>
Status: CLOSED ERRATA QA Contact: atomic-bugs <atomic-bugs>
Severity: high Docs Contact:
Priority: unspecified    
Version: 7.3CC: amurdaca, dwalsh, lsm5
Target Milestone: rcKeywords: Extras
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
Their was a race condition where the docker daemon could hang under load. This version fixes this race condition.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2017-05-26 14:52:04 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1298243    
Attachments:
Description Flags
Hung dockerd core file generated by gcore
none
Backtrace from all goroutines of hung dockerd none

Description Sergio Lopez 2017-04-27 12:12:15 UTC 
Created attachment 1274607 [details]
Hung dockerd core file generated by gcore

Description of problem:

On a Docker environment with Cluster Store, Cluster Advertise, and some Overlay networks, if an EventMemberJoin event is received while processing a Node found in KV store, dockerd process hangs indefinitely.


Version-Release number of selected component (if applicable):

Tested with docker-1.12.6-11.el7.x86_64


How reproducible:

Sometimes, depends on Nodes coordination.


Steps to Reproduce:
1. Prepare a 3 node Docker environment with Cluster Store and Cluster Advertise.
2. Create some Overlay Networks.
3. Create a few containers with an automatic restart policy.
4. Restart dockerd a few times.


Actual results:

dockerd becomes unresponsive (service socket is created, but doesn't answer to connection requests).


Expected results:

dockerd shouldn't hang.


Additional info:

The root cause is that peerDbNetworkWalk iterates through the map calling the passed function while holding pMap.Lock. One of the functions passed to peerDbNetworkWalk is pushLocalEndpointEvent, which sends an event to the serf channel.

Meanwhile, if an EventMemberJoin event has been received by ov_serf event channel, it will eventually call peerAdd, which tries to hold the same pMap.Lock.

So we have startSerfLoop busy waiting for pMap.Lock to be released, and peerDbNetworkWalk holding the lock while waiting in pushLocalEndpointEvent, causing the deadlock.

This has been addressed upstream by this commit: https://github.com/docker/libnetwork/commit/760abd041b3100007987423140db1f169c84dab9
Comment 2 Sergio Lopez 2017-04-27 12:14:42 UTC 
Created attachment 1274608 [details]
Backtrace from all goroutines of hung dockerd
Comment 3 Sergio Lopez 2017-04-27 12:18:54 UTC 
docker-1.12.6-16 from RHEL 7.3 is also affected since Project Atomic's libnetwork commit level is behind upstream.
Comment 4 Antonio Murdaca 2017-04-27 12:42:06 UTC 
Fixed in docker-1.12.6 via https://github.com/projectatomic/docker/commit/c14458a6b1955fc2a6793eea297b43821837285a
Comment 5 Antonio Murdaca 2017-04-27 12:47:38 UTC 
Fixed in docker-1.13.1 as well, FYI
Comment 8 errata-xmlrpc 2017-05-26 14:52:04 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2017:1325