netdev - [Patch v4 net 0/6] netem: Fix skb duplication logic and prevent infinite loops

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Message-Id: <20250719220341.1615951-1-xiyou.wangcong@gmail.com>
Date: Sat, 19 Jul 2025 15:03:35 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: netdev@...r.kernel.org
Cc: jhs@...atatu.com,
	will@...lsroot.io,
	stephen@...workplumber.org,
	Cong Wang <xiyou.wangcong@...il.com>
Subject: [Patch v4 net 0/6] 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 replaces the patches from William, with much less code and without
any workaround. More importantly, this does not break any use case.

All the test cases pass with this patchset.

---
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 (6):
  net_sched: Implement the right netem duplication behavior
  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                         |  26 ++--
 net/sched/sch_qfq.c                           |   2 +
 .../tc-testing/tc-tests/infra/qdiscs.json     | 114 +++++++++++++-----
 .../tc-testing/tc-tests/qdiscs/netem.json     |  25 ++++
 4 files changed, 127 insertions(+), 40 deletions(-)

-- 
2.34.1