Victor Nogueria 1b9bc71153 net/sched: sch_sfb: Replace direct dequeue call with peek and qdisc_dequeue_peeked
When sfb has children (eg qfq qdisc) whose peek() callback is
qdisc_peek_dequeued(), we could get a kernel panic. When the parent of such
qdiscs (eg illustrated in patch #3 as tbf) wants to retrieve an skb from
its child (sfb in this case), it will do the following:
 1a. do a peek() - and when sensing there's an skb the child can offer, then
     - the child in this case(sfb) calls its child's (qfq) peek.
        qfq does the right thing and will return the gso_skb queue packet.
        Note: if there wasnt a gso_skb entry then qfq will store it there.
 1b. invoke a dequeue() on the child (sfb). And herein lies the problem.
     - sfb will call the child's dequeue() which will essentially just
       try to grab something of qfq's queue.

[  127.594489][  T453] KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f]
[  127.594741][  T453] CPU: 2 UID: 0 PID: 453 Comm: ping Not tainted 7.1.0-rc1-00035-gac961974495b-dirty #793 PREEMPT(full)
[  127.595059][  T453] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  127.595254][  T453] RIP: 0010:qfq_dequeue+0x35c/0x1650 [sch_qfq]
[  127.595461][  T453] Code: 00 fc ff df 80 3c 02 00 0f 85 17 0e 00 00 4c 8d 73 48 48 89 9d b8 02 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 f2 48 c1 ea 03 <80> 3c 02 00 0f 85 76 0c 00 00 48 b8 00 00 00 00 00 fc ff df 4c 8b
[  127.596081][  T453] RSP: 0018:ffff88810e5af440 EFLAGS: 00010216
[  127.596337][  T453] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: dffffc0000000000
[  127.596623][  T453] RDX: 0000000000000009 RSI: 0000001880000000 RDI: ffff888104fd82b0
[  127.596917][  T453] RBP: ffff888104fd8000 R08: ffff888104fd8280 R09: 1ffff110211893a3
[  127.597165][  T453] R10: 1ffff110211893a6 R11: 1ffff110211893a7 R12: 0000001880000000
[  127.597404][  T453] R13: ffff888104fd82b8 R14: 0000000000000048 R15: 0000000040000000
[  127.597644][  T453] FS:  00007fc380cbfc40(0000) GS:ffff88816f2a8000(0000) knlGS:0000000000000000
[  127.597956][  T453] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  127.598160][  T453] CR2: 00005610aa9890a8 CR3: 000000010369e000 CR4: 0000000000750ef0
[  127.598390][  T453] PKRU: 55555554
[  127.598509][  T453] Call Trace:
[  127.598629][  T453]  <TASK>
[  127.598718][  T453]  ? mark_held_locks+0x40/0x70
[  127.598890][  T453]  ? srso_alias_return_thunk+0x5/0xfbef5
[  127.599053][  T453]  sfb_dequeue+0x88/0x4d0
[  127.599174][  T453]  ? ktime_get+0x137/0x230
[  127.599328][  T453]  ? srso_alias_return_thunk+0x5/0xfbef5
[  127.599480][  T453]  ? qdisc_peek_dequeued+0x7b/0x350 [sch_qfq]
[  127.599670][  T453]  ? srso_alias_return_thunk+0x5/0xfbef5
[  127.599831][  T453]  tbf_dequeue+0x6b1/0x1098 [sch_tbf]
[  127.599988][  T453]  __qdisc_run+0x169/0x1900

The right thing to do in #1b is to grab the skb off gso_skb queue.
This patchset fixes that issue by changing #1b to use qdisc_dequeue_peeked()
method instead.

Fixes: e13e02a3c6 ("net_sched: SFB flow scheduler")
Signed-off-by: Victor Nogueria <victor@mojatatu.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260430152957.194015-3-jhs@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2026-05-02 10:20:56 -07:00
2026-01-26 19:07:09 -08:00
2022-09-28 09:02:20 +02:00
2025-02-19 14:53:27 -07:00
2026-04-26 14:19:00 -07:00

Linux kernel
============

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros
* AI Coding Assistant - LLMs and AI-powered development tools


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst

AI Coding Assistant
-------------------

CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and
follow the AI coding assistants documentation before contributing to the Linux
kernel:

* Documentation/process/coding-assistants.rst

This documentation contains essential requirements about licensing, attribution,
and the Developer Certificate of Origin that all AI tools must comply with.


Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst
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