[Patch net v7 0/9] netem: Fix skb duplication logic and prevent infinite loops

[Cong Wang <xiyou.wangcong@gmail.com>]

This patchset fixes the infinite loops due to duplication in netem, the
real root cause of this problem is enqueuing to the root qdisc, which is
now changed to enqueuing to the same qdisc. This is more reasonable,
more intuitive from users' perspective, less error-prone and more elegant
from kernel developers' perspective.

Please see more details in patch 4/9 which contains two pages of detailed
explanation including why it is safe and better.

This reverts the offending commits from William which clearly broke
mq+netem use cases, as reported by two users.

All the TC test cases pass with this patchset.

---
v7: Fixed a typo in subject
    Fixed a missing qdisc_tree_reduce_backlog()
    Added a new selftest for backlog validation

v6: Dropped the init_user_ns check patch
    Reordered the qfq patch
    Rebased to the latest -net branch

v5: Reverted the offending commits
    Added a init_user_ns check (4/9)
    Rebased to the latest -net branch

v4: Added a fix for qfq qdisc (2/6)
    Updated 1/6 patch description
    Added a patch to update the enqueue reentrant behaviour tests

v3: Fixed the root cause of enqueuing to root
    Switched back to netem_skb_cb safely
    Added two more test cases

v2: Fixed a typo
    Improved tdc selftest to check sent bytes

Cong Wang (9):
  net_sched: Check the return value of qfq_choose_next_agg()
  Revert "net/sched: Restrict conditions for adding duplicating netems
    to qdisc tree"
  Revert "selftests/tc-testing: Add tests for restrictions on netem
    duplication"
  net_sched: Implement the right netem duplication behavior
  selftests/tc-testing: Add a nested netem duplicate test
  selftests/tc-testing: Add a test case for prio with netem duplicate
  selftests/tc-testing: Add a test case for mq with netem duplicate
  selftests/tc-testing: Update test cases with netem duplicate
  selftests/tc-testing: Add a test case for HTB with netem

 net/sched/sch_netem.c                         |  67 ++------
 net/sched/sch_qfq.c                           |   2 +
 .../tc-testing/tc-tests/infra/qdiscs.json     | 148 ++++++++++++++----
 .../tc-testing/tc-tests/qdiscs/netem.json     |  90 ++---------
 4 files changed, 155 insertions(+), 152 deletions(-)

-- 
2.34.1