[Bug 1577844] Re: Drop unnecessary blocking of all net udev rules
smoser at ubuntu.com
Mon May 9 18:44:53 UTC 2016
** Changed in: cloud-init (Ubuntu)
Importance: Undecided => Medium
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Drop unnecessary blocking of all net udev rules
Status in cloud-init package in Ubuntu:
Status in ifupdown package in Ubuntu:
cloud-inits networking setup currently jumps through a lot of bad
hoops to make sure that ifup@ does not run until after cloud-init-
local.service. This includes blocking udev rules for an indefinite
time, which is racy, a potential deadlock, and highly non-elegant.
This is also not necessary: while ifupdown's net udev rule certainly
can fire before cloud-init-local, it only asynchronously starts
ifup at .service which will be deferred until after network-pre.target
and thus after cloud-init-local.service.
Original description, which turned out to be completely false and just us being misled:
ifup at .service can (and often does) run for a particular interface
before networking.service runs. This is brittle as during early boot
ifup is prone to fail: / might still be read-only, /var might not yet
exist or be writable, dhclient-enter-hooks.d/ or if-up.d/ hooks might
silently fail, etc. It is also unnecessary as networking.service will
bring up all "auto" and all present "allow-hotplug" interfaces anyway,
and it runs at the right time.
We should make either 80-ifupdown.rules or ifup at .service ignore events
until networking.service is active, or wait until after it has run
(slower, but avoids race conditions when hotplug events happen while
networking.service is running). Thus we need to add
After=networking.service to ifup at .service, so that this only does
stuff after doing the "coldplug" configuration.
This also affects cloud-init's setup of networking: this currently
jumps through a lot of bad hoops to make sure that ifup@ does not run
until after cloud-init-local.service. This includes blocking udev
rules for an indefinite time, which is racy, a potential deadlock, and
https://bugs.debian.org/752919 is related to this issue.
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