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Willem de Bruijn c4f796c4f1 net_sched: sch_fq: convert skb->tstamp if not monotonic
FQ currently assumes skb->tstamp holds monotonic time, as used by TCP.

Users with ns_capable CAP_NET_ADMIN can transmit skbs using SO_TXTIME
with CLOCK_MONOTONIC, CLOCK_REALTIME or CLOCK_TAI clockids as of
commit 80b14dee2b ("net: Add a new socket option for a future
transmit time.")

More recently, skbs also gained tstamp_type to explicitly communicate
the clockid of skb->tstamp, with commit 4d25ca2d68 ("net: Rename
mono_delivery_time to tstamp_type for scalabilty"), commit
1693c5db6a ("net: Add additional bit to support clockid_t timestamp
type") and a few others.

Detect other clocks and convert to monotonic for use in FQ. That is,
convert fq_skb_cb(skb)->time_to_send. Do not convert skb->tstamp
itself. Network device clocks are more commonly synchronized to TAI.

Conversion may be imprecise due to clock adjustment (e.g., adjfreq)
between when SCM_TSTAMP is set and when it is converted in fq_enqueue.
The common codepath is short, so skew will be well below common pacing
operation. Even in edge cases, bursts (too soon) or beyond horizon
(too late) are indistinguishable from network conditions. To which
senders must be robust, as long as infrequent.

Avoid overflow due to negative offsets becoming huge when converting
from signed ktime_t to u64 time_to_send. Bound lower to mono 1 and
upper to now + q->horizon. This protects against bad input, e.g.,
from BPF programs.

Detect legacy BPF programs that program skb->tstamp without setting
skb->tstamp_type. Here tstamp_type is zero (SKB_CLOCK_REALTIME), but
the value will be unrealistic for realtime in the 21st century. Follow
existing TIME_UPTIME_SEC_MAX as bound between mono and realtime.

Signed-off-by: Willem de Bruijn <willemb@google.com>

----

Changes
  v1 -> v2
    - replace Fixes tag with references inside the commit message

Link: https://patch.msgid.link/20260604194221.3319080-3-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2026-06-08 16:00:06 -07:00
arch Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2026-06-04 15:29:04 -07:00
block block-7.1-20260529 2026-05-29 10:41:07 -07:00
certs Clang build fixes for 7.1 2026-04-24 09:29:51 -07:00
crypto crypto: api - Fold crypto_alloc_tfmmem() into crypto_create_tfm_node() 2026-05-28 17:45:46 -07:00
Documentation netfilter pull request 26-06-07 2026-06-08 15:33:35 -07:00
drivers geneve: Move udp_conf.local_ip6 under CONFIG_IPV6 in geneve_create_sock(). 2026-06-08 15:58:16 -07:00
fs two client fixes 2026-05-30 17:05:58 -07:00
include This cleanup patchset includes the following patches, all by 2026-06-08 15:40:55 -07:00
init memblock: updates for 7.0-rc1 2026-04-18 11:29:14 -07:00
io_uring io_uring-7.1-20260529 2026-05-29 10:36:57 -07:00
ipc ipc: limit next_id allocation to the valid ID range 2026-05-21 19:06:11 -07:00
kernel cgroup: Fixes for v7.1-rc6 2026-06-03 08:59:24 -07:00
lib IOMMU Fixes for Linux v7.1-rc5 2026-05-29 09:25:58 -07:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
mm 13 hotfixes. All are for MM. 10 are cc:stable and the remaining 3 2026-06-02 08:59:35 -07:00
net net_sched: sch_fq: convert skb->tstamp if not monotonic 2026-06-08 16:00:06 -07:00
rust Rust fixes for v7.1 2026-05-09 11:24:02 -07:00
samples soc: drivers for 7.1 2026-04-16 20:34:34 -07:00
scripts Second round of Kbuild fixes for 7.1 2026-05-19 09:43:24 -07:00
security security/keys: fix missed RCU read section on lookup 2026-05-28 11:45:41 -07:00
sound ASoC: Fixes for v7.1 2026-05-28 13:48:04 +02:00
tools selftests: drv-net: add userns devmem RX test 2026-06-05 18:10:31 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt KVM: Reject wrapped offset in kvm_reset_dirty_gfn() 2026-05-12 22:16:16 +02:00
.clang-format Devicetree updates for v7.0: 2026-02-11 18:27:08 -08:00
.clippy.toml rust: bump Clippy's MSRV and clean incompatible_msrv allows 2026-04-07 09:51:39 +02:00
.cocciconfig
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add myself 2026-04-02 16:48:25 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rust: provide an option to inline C helpers into Rust 2026-03-30 02:03:52 +02:00
.mailmap 13 hotfixes. 9 are for MM. 9 are cc:stable and the remaining 4 address 2026-05-26 08:23:19 -07:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING
CREDITS Delete some obsolete networking code 2026-04-24 09:41:58 -07:00
Kbuild checksyscalls: move instance functionality into generic code 2026-04-05 09:21:32 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2026-06-04 15:29:04 -07:00
Makefile Linux 7.1-rc6 2026-05-31 15:14:24 -07:00
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -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