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Alexei Starovoitov 0d6bc03d73 Merge branch 'bpf-expand-the-usage-scenarios-of-bpf_kptr_xchg'
Kaitao Cheng says:

====================
When using bpf_kptr_xchg, we triggered the following error:
    31: (85) call bpf_kptr_xchg#194
    function calls are not allowed while holding a lock
bpf_kptr_xchg can now be used in lock-held contexts, so we extended
its usage scope in [patch 1/5].

When writing test cases using bpf_kptr_xchg and bpf_rbtree_*, the
following approach must be followed:

	bpf_spin_lock(&lock);
	rb_n = bpf_rbtree_root(&root);
	while (rb_n && can_loop) {
		rb_n = bpf_rbtree_remove(&root, rb_n);
		if (!rb_n)
			goto fail;

		tnode = container_of(rb_n, struct tree_node, node);
		node_data = bpf_kptr_xchg(&tnode->node_data, NULL);
		if (!node_data)
			goto fail;

		data = node_data->data;
		/* use data to do something */

		node_data = bpf_kptr_xchg(&tnode->node_data, node_data);
		if (node_data)
			goto fail;

		bpf_rbtree_add(&root, rb_n, less);

		if (lookup_key < tnode->key)
			rb_n = bpf_rbtree_left(&root, rb_n);
		else
			rb_n = bpf_rbtree_right(&root, rb_n);
	}
	bpf_spin_unlock(&lock);

The above illustrates a lock-remove-read-add-unlock workflow, which
exhibits lower performance. To address this, we introduced support
for a streamlined lock-read-unlock operation in [patch 2/5] and
[patch 4/5].

Changes in v7:
- Add a comma to the variable declaration in enum bpf_reg_type
- Modify the prefixes
Changes in v6:
- allow using bpf_kptr_xchg even if the MEM_RCU flag is set
- Add test case
Changes in v5:
- add lastname
Changes in v4:
- Fix the dead logic issue in the test case
Changes in v3:
- Fix compilation errors
Changes in v2:
- Allow using bpf_kptr_xchg even if the NON_OWN_REF flag is set
- Add test case

Link to v6:
https://lore.kernel.org/all/20260208024846.18653-1-pilgrimtao@gmail.com/
Link to v5:
https://lore.kernel.org/all/20260203022712.99347-1-pilgrimtao@gmail.com/
Link to v4:
https://lore.kernel.org/all/20260202090051.87802-1-pilgrimtao@gmail.com/
Link to V3:
https://lore.kernel.org/all/20260202055818.78231-1-pilgrimtao@gmail.com/
Link to V2:
https://lore.kernel.org/all/20260201031607.32940-1-pilgrimtao@gmail.com/
Link to V1:
https://lore.kernel.org/all/20260122081426.78472-1-pilgrimtao@gmail.com/
====================

Link: https://patch.msgid.link/20260214124042.62229-1-pilgrimtao@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
History 2026-02-23 17:37:21 -08:00
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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