[Bug 1961697] Re: Transaction ID collisions cause slow DNS lookups in getaddrinfo
KJ Tsanaktsidis
1961697 at bugs.launchpad.net
Mon Nov 21 07:00:02 UTC 2022
I ran into this issue in production today on Graviton 3 AWS instances
(with Bionic) :(
Did this ever get backported to Focal, at least? It definitely doesn't
seem to be currently fixed in Bionic still.
This program seems to semi-reliably trip the problem up, but again it's
very non-deterministic. I don't know if this helps with a reproduction?
https://gist.github.com/KJTsanaktsidis/668247fd898cec57f9d280b0222438ae
--
You received this bug notification because you are a member of Ubuntu
Foundations Bugs, which is subscribed to glibc in Ubuntu.
https://bugs.launchpad.net/bugs/1961697
Title:
Transaction ID collisions cause slow DNS lookups in getaddrinfo
Status in GLibC:
Fix Released
Status in glibc package in Ubuntu:
Confirmed
Status in glibc source package in Focal:
New
Bug description:
[impact]
When resolving DNS names with getaddrinfo(), I have seen this hang for 5 seconds and then retry and succeed. The issue is that glibc will issue a both an A and AAAA query on the same socket, and in some circumstances they can be sent with the same DNS transaction ID as well.
[test case]
TBD
[regression potential]
TBD.
[original description]
I verified this with a packet capture; in the packet capture, I saw the A and AAAA queries for a name be made with the same DNS transaction ID, get responses, do nothing for five seconds, and then send the same DNS query again. On the glibc side, I confirmed that it's blocked waiting for the DNS response by interrupting it with gdb, even though the packet capture shows the response has well and truly arrived. I've attached a packet capture & a backtrace of the glibc hang.
I believe this is the same issue reported in these places:
* In RHEL: https://bugzilla.redhat.com/show_bug.cgi?id=1904153
* Also RHEL: https://bugzilla.redhat.com/show_bug.cgi?id=1903880
* Upstream: https://sourceware.org/bugzilla/show_bug.cgi?id=26600
The environment I noticed this bug in was:
* Docker for Mac on an arm64 m1 Macbook
* Docker for Mac Linux kernel version is 5.10.76-linuxkit
* Linux is also arm64, not emulated
* Container with the buggy DNS environment is Ubuntu bionic (also arm64, not emulated)
* Glibc 2.27-3ubuntu1.4
However one of the redhat reporters noticed this issue in m6 series
EC2 instances in AWS.
A patch has been provided upstream for this issue:
https://sourceware.org/pipermail/libc-alpha/2020-September/117547.html
I applied the upstream patch to glibc 2.27-3ubuntu1.4 and rebuilt the
package, and the problem went away. I've attached the exact patch I
applied, since I had to work through some conflicts.
So, I think that patch just needs to be backported to Bionic and (I
think) Focal as well. Is that reasonable?
Thanks!
To manage notifications about this bug go to:
https://bugs.launchpad.net/glibc/+bug/1961697/+subscriptions
More information about the foundations-bugs
mailing list