netdev - [Patch net v5 0/9] netem: Fix skb duplication logic and prevent infinite loops

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Message-Id: <20251126195244.88124-1-xiyou.wangcong@gmail.com>
Date: Wed, 26 Nov 2025 11:52:35 -0800
From: Cong Wang <xiyou.wangcong@...il.com>
To: netdev@...r.kernel.org
Cc: stephen@...workplumber.org,
	kuba@...nel.org,
	Cong Wang <xiyou.wangcong@...il.com>
Subject: [Patch net v5 0/9] netem: Fix skb duplication logic and prevent infinite loops

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 predictable from users' perspective, less error-proone and more elegant.

Please see more details in patch 1/6 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.

All the test cases pass with this patchset.

---
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):
  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
  net_sched: Prevent using netem duplication in non-initial user
    namespace
  net_sched: Check the return value of qfq_choose_next_agg()
  selftests/tc-testing: Add a nested netem duplicate test
  selftests/tc-testing: Add a test case for piro with netem duplicate
  selftests/tc-testing: Add a test case for mq with netem duplicate
  selftests/tc-testing: Update test cases with netem duplicate

 net/sched/sch_netem.c                         |  72 ++++-------
 net/sched/sch_qfq.c                           |   2 +
 .../tc-testing/tc-tests/infra/qdiscs.json     | 115 +++++++++++++-----
 .../tc-testing/tc-tests/qdiscs/netem.json     |  90 +++-----------
 4 files changed, 126 insertions(+), 153 deletions(-)

-- 
2.34.1