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| author | Jesper Dangaard Brouer <brouer@redhat.com> | 2016-11-03 16:56:11 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2016-11-08 04:15:55 +0300 |
| commit | 84c46dd865384a1613e797b967552e4a428b5202 (patch) | |
| tree | fd0201d39d33a237267cf9c0ca62166e3b246469 /net/sched | |
| parent | 1159708432f7067b82388695e29d7105e79bd293 (diff) | |
| download | linux-84c46dd865384a1613e797b967552e4a428b5202.tar.xz | |
qdisc: catch misconfig of attaching qdisc to tx_queue_len zero device
It is a clear misconfiguration to attach a qdisc to a device with
tx_queue_len zero, because some qdisc's (namely, pfifo, bfifo, gred,
htb, plug and sfb) inherit/copy this value as their queue length.
Why should the kernel catch such a misconfiguration? Because prior to
introducing the IFF_NO_QUEUE device flag, userspace found a loophole
in the qdisc config system that allowed them to achieve the equivalent
of IFF_NO_QUEUE, which is to remove the qdisc code path entirely from
a device. The loophole on older kernels is setting tx_queue_len=0,
*prior* to device qdisc init (the config time is significant, simply
setting tx_queue_len=0 doesn't trigger the loophole).
This loophole is currently used by Docker[1] to get better performance
and scalability out of the veth device. The Docker developers were
warned[1] that they needed to adjust the tx_queue_len if ever
attaching a qdisc. The OpenShift project didn't remember this warning
and attached a qdisc, this were caught and fixed in[2].
[1] https://github.com/docker/libcontainer/pull/193
[2] https://github.com/openshift/origin/pull/11126
Instead of fixing every userspace program that used this loophole, and
forgot to reset the tx_queue_len, prior to attaching a qdisc. Let's
catch the misconfiguration on the kernel side.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/sched')
| -rw-r--r-- | net/sched/sch_api.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c index 206dc24add3a..f337f1bdd1d4 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -960,6 +960,17 @@ static struct Qdisc *qdisc_create(struct net_device *dev, sch->handle = handle; + /* This exist to keep backward compatible with a userspace + * loophole, what allowed userspace to get IFF_NO_QUEUE + * facility on older kernels by setting tx_queue_len=0 (prior + * to qdisc init), and then forgot to reinit tx_queue_len + * before again attaching a qdisc. + */ + if ((dev->priv_flags & IFF_NO_QUEUE) && (dev->tx_queue_len == 0)) { + dev->tx_queue_len = DEFAULT_TX_QUEUE_LEN; + netdev_info(dev, "Caught tx_queue_len zero misconfig\n"); + } + if (!ops->init || (err = ops->init(sch, tca[TCA_OPTIONS])) == 0) { if (qdisc_is_percpu_stats(sch)) { sch->cpu_bstats = |