Public bug reported:
I have the following in my /etc/network/interfaces to configure a GRE-
TAP tunnel and attach it to a bridge:
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet static
address 10.11.12.13
netmask 255.255.255.0
gateway 10.11.12.1
auto l2gre0
iface l2gre0 inet manual
pre-up ip link add name $IFACE type gretap local 10.11.12.13 remote
10.13.14.15
up ip link set dev $IFACE up
down ip link set dev $IFACE down
post-down ip link delete $IFACE
auto sw0
iface sw0 inet manual
pre-up ip link set dev eth1 promisc on
bridge_ports eth1 l2gre0
bridge_stp off
bridge_fd 0.1
bridge_maxwait 0
post-up sysctl -q net.ipv4.conf.sw0.rp_filter=0
I've found that on reboot, about 50% of the time the bridge comes up
fine, and about 50% of the time the bridge comes up half-configured (it
has l2gre0 attached but not eth1, and the stp and fd settings are not
configured). When it fails, device sw0 already exists; can't create
bridge with the same name shows up in the logs.
The problem seems to be a race condition between /lib/bridge-utils/ifupdown.sh
and /lib/udev/bridge-network-interface ... The sequence of events is the
following:
udev event triggered for eth0
udev event triggered for eth1 (ignored by bridge-network-interface because
/run/network doesn't exist yet)
udev event triggered for lo
ifup called for eth0
ifup called for lo
ifup called for l2gre0
Then, the following two operations happen in parallel:
udev event triggered for l2gre0
ifup called for sw0
If ifup happens to reach the 'brctl addbr' command in
/lib/bridge-utils/ifupdown.sh first, everything works fine. However, if the
udev trigger happens to reach the 'brctl addbr' command in
/lib/udev/bridge-network-interface first, then /lib/bridge-utils/ifupdown.sh
will fail, and the bridge will not be properly configured.
This race condition appears to have been introduced by the fix for Bug
#1003656 ... Before that fix, /lib/udev/bridge-network-interface would
call 'ifup sw0' instead of just 'brctl addbr sw0', and 'ifup sw0' would
ensure that only one of the two threads called 'brctl addbr'.
As for fixing this problem, I can't say that I'm aware of every possible
use case here, but it seems to me that /lib/udev/bridge-network-
interface simply should not call 'brctl addbr'. According to
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=626152 this udev
trigger was added to ensure that devices are properly added to the
bridge if the bridge happens to come up before all of the physical
network interfaces have been probed by the kernel. However, if
/lib/udev/bridge-network-interface is called before the bridge comes up,
shouldn't it simply ignore the event and let /lib/bridge-
utils/ifupdown.sh bring the bridge up and add the interface later?
** Affects: bridge-utils (Ubuntu)
Importance: Undecided
Status: New
--
You received this bug notification because you are a member of Ubuntu
Server Team, which is subscribed to bridge-utils in Ubuntu.
https://bugs.launchpad.net/bugs/1294172
Title:
Race condition between bridge-utils pre-up and udev scripts
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/bridge-utils/+bug/1294172/+subscriptions
--
Ubuntu-server-bugs mailing list
Ubuntu-server-bugs@lists.ubuntu.com
Modify settings or unsubscribe at:
https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
