[0/4] sched: Fix qdisc interactions exposed by using sch_cake as a leaf qdisc

This series fixes a couple of issues exposed by running sch_cake as a
leaf qdisc in an HFSC tree, which were discovered and reported by Pete
Heist. The interaction between CAKE's GSO splitting and the parent
qdisc's notion of its own queue length could cause queue stalls. While
investigating the report, I also noticed that several qdiscs would
dereference the skb pointer after dequeue, which is potentially
problematic since the GSO splitting code also frees the original skb.

See the individual patches in the series for details.

Toke Høiland-Jørgensen (4):
  sched: Avoid dereferencing skb pointer after child enqueue
  sched: Fix detection of empty queues in child qdiscs
  sch_api: Allow reducing queue backlog by a negative value
  sch_cake: Correctly update parent qlen when splitting GSO packets

 include/net/sch_generic.h |  3 +--
 net/sched/sch_api.c       |  3 +--
 net/sched/sch_cake.c      |  5 +++--
 net/sched/sch_cbs.c       |  3 ++-
 net/sched/sch_drr.c       |  7 +++++--
 net/sched/sch_dsmark.c    |  3 ++-
 net/sched/sch_hfsc.c      |  9 +++++----
 net/sched/sch_htb.c       |  3 ++-
 net/sched/sch_prio.c      |  3 ++-
 net/sched/sch_qfq.c       | 20 ++++++++++++--------
 net/sched/sch_tbf.c       |  3 ++-
 11 files changed, 37 insertions(+), 25 deletions(-)

From: Toke Høiland-Jørgensen <toke@toke.dk>
Date: Mon,  7 Jan 2019 20:47:29 +0100

> This series fixes a couple of issues exposed by running sch_cake as a
> leaf qdisc in an HFSC tree, which were discovered and reported by Pete
> Heist. The interaction between CAKE's GSO splitting and the parent
> qdisc's notion of its own queue length could cause queue stalls. While
> investigating the report, I also noticed that several qdiscs would
> dereference the skb pointer after dequeue, which is potentially
> problematic since the GSO splitting code also frees the original skb.
> 
> See the individual patches in the series for details.

Toke, can you please resubmit this without patch #3.

If you want to push for patch #3 still, it is much easier to submit
it separately.

David Miller <davem@davemloft.net> writes:

> From: Toke Høiland-Jørgensen <toke@toke.dk>
> Date: Mon,  7 Jan 2019 20:47:29 +0100
>
>> This series fixes a couple of issues exposed by running sch_cake as a
>> leaf qdisc in an HFSC tree, which were discovered and reported by Pete
>> Heist. The interaction between CAKE's GSO splitting and the parent
>> qdisc's notion of its own queue length could cause queue stalls. While
>> investigating the report, I also noticed that several qdiscs would
>> dereference the skb pointer after dequeue, which is potentially
>> problematic since the GSO splitting code also frees the original skb.
>> 
>> See the individual patches in the series for details.
>
> Toke, can you please resubmit this without patch #3.
>
> If you want to push for patch #3 still, it is much easier to submit
> it separately.

Can do :)

-Toke