Red Hat Bugzilla – Bug 143117
sfq qdisc doesn't dequeue packets after a while
Last modified: 2015-01-04 17:14:05 EST
Description of problem:
sfq qdisc stops dequeuing packets under load (hangs), causing
complete network outage for all packets assigned to the class to
which this sfq qdisc belongs.
If I replace the sfq's by pfifo's the problem never shows, so,
although I am not absolutely sure, I strongly think the problem is
situated in sfq.
Version-Release number of selected component (if applicable):
Under high load, always within half an hour (checked on two different
systems with rather different LAN adapters (1 Intel 10/100/100, 1
Steps to Reproduce:
1. Execute the attached shell script on a router at one side attached
to the Internet via a high speed connection (in my case cable, and in
the second setup a 2Mbit serial connection), and at the other side a
10/100 Ethernet switch. The $x parameter is supposed to be the name
of the interface at the "inside".
2. Surf around on the Internet, download some things, preferrable
with multiple flows, on a PC that uses this router to get to the
Internet and that make the packets end up in the sfq qdisc on the
router. After a while, all connections will drop. Pings to that host
won't work anymore if the echo-reply packets are scheduled to the sfq
qdisc that hangs (but the other sfq's attached to sibling classes
will keep working normally. I checked this by pinging from that
router by setting different QoS bits in the echo-request packet (see
At the moment sfq decides to stop dequeuing packets 'tc' shows that
there are 126 packets enqueued, always. Any new packet is dropped
immediately (or replaces a packet in the sfq, don't know how the
queuing exactly works). It remains in this situation forever, until
the hanging qdisc is deleted (or the root qdisc). Maybe I haven't
waited long enough, but I have waited minutes to see if the problem
would solve itself.
Created attachment 108721 [details]
script to create a QoS infrastructure, exhibits sfq problem
An update has been released for Fedora Core 3 (kernel-2.6.12-1.1372_FC3) which
may contain a fix for your problem. Please update to this new kernel, and
report whether or not it fixes your problem.
If you have updated to Fedora Core 4 since this bug was opened, and the problem
still occurs with the latest updates for that release, please change the version
field of this bug to 'fc4'.
This bug has been automatically closed as part of a mass update.
It had been in NEEDINFO state since July 2005.
If this bug still exists in current errata kernels, please reopen this bug.
There are a large number of inactive bugs in the database, and this is the only
way to purge them.