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Linus Torvalds a7f2bc8787 RCU updates:
Execution contexts and call_rcu() and call_srcu():
  * Make call_rcu() and call_srcu invocable from NMI handlers and while
    holding scheduler locks (using irq-work handlers).
  * Add rcutorture and BPF tests calling these functions from these
    contexts.
  * Disable rcutorture overload testing for RCU readers that are "fragile",
    that is, that do not either disable preemption or have some form of
    RCU priority boosting.
 
 SRCU updates:
  * Add an atomic SRCU where readers run with preemption disabled and
    grace periods can be invoked from atomic contexts.  David Woodhouse
    has a patch series exploiting this for GPC.
  * Add torture and lockdep tests for atomic SRCU.
  * Add numerous optimizations for atomic SRCU based on the fact that it
    does not have callbacks, for example, eliminating any transition to
    "big" srcu_struct structures even on systems that configure these to
    happen at initialization time.
 
 Additional torture-test updates:
  * Fix a divide-by-zero bug in forward-progress testing.
  * Synchronously wait for all IRQ-queued callbacks to complete.
  * Allow alternative "ssh" commands to be specified for use by
    kvm-remote.sh.
  * Fix kvm-again.sh re-run failure on PowerPC.
  * Add additional lockdep testing for atomic SRCU.
  * Fix error double-counting in srcu_lockdep.sh.
  * Add atomic SRCU cross-CPU IRQ context mismatch testing, with the
  * trick being that the atomic SRCU readers context must be at least as
    strict as that of the atomic SRCU grace-period wait.  So for example,
    if the readers have IRQs disabled, so must the grace-period wait.
 
 Miscellaneous updates:
  * Update stallwarn.rst documentation for the re-implementation of RCU
    Tasks Trace in terms of SRCU.
  * Fix the lazy-callback shrink scanner budget computation so that it
    honors the reclaim budget.
  * Avoid panicking on RCU CPU stalls that end before the warning can
    be printed.
  * Add "running" and "boosted" indications to the RCU task stall warning
    output.
  * People have been (incorrectly) relying on rcu_barrier() to wait for
    kfree_rcu() callbacks and processing.  But it turns out to be easier to
    fix rcu_barrier() to meet their expectations than to fix their code to
    live within the earlier rcu_barrier() specification.  So rcu_barrier()
    now waits on kfree_rcu() callbacks and processing.
  * Disable RCU Tasks console output that track when this RCU flavor
    switches between per-CPU and global callback queuing.  New use cases
    appeared that generated enough console traffic to cause trouble, and
    no one seemed to care about these messages.  For those needing those
    messages, there is a new rcupdate.rcu_task_collapse_debug kernel boot
    parameter.
  * Fix __rcu pointer attribute handling to eliminate false positives.
  * Fix typos and drop redundant #include directives.
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Merge tag 'rcu.2026.10.12b' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux

Pull RCU updates from Paul McKenney:
 "Execution contexts and call_rcu() and call_srcu():
   - Make call_rcu() and call_srcu invocable from NMI handlers and while
     holding scheduler locks (using irq-work handlers)
   - Add rcutorture and BPF tests calling these functions from these
     contexts
   - Disable rcutorture overload testing for RCU readers that are
     "fragile", that is, that do not either disable preemption or have
     some form of RCU priority boosting

  SRCU updates:
   - Add an atomic SRCU where readers run with preemption disabled and
     grace periods can be invoked from atomic contexts. David Woodhouse
     has a patch series exploiting this for GPC
   - Add torture and lockdep tests for atomic SRCU
   - Add numerous optimizations for atomic SRCU based on the fact that
     it does not have callbacks, for example, eliminating any transition
     to "big" srcu_struct structures even on systems that configure
     these to happen at initialization time

  Additional torture-test updates:
   - Fix a divide-by-zero bug in forward-progress testing
   - Synchronously wait for all IRQ-queued callbacks to complete
   - Allow alternative "ssh" commands to be specified for use by
     kvm-remote.sh
   - Fix kvm-again.sh re-run failure on PowerPC
   - Add additional lockdep testing for atomic SRCU
   - Fix error double-counting in srcu_lockdep.sh
   - Add atomic SRCU cross-CPU IRQ context mismatch testing, with the
   - trick being that the atomic SRCU readers context must be at least
     as strict as that of the atomic SRCU grace-period wait. So for
     example, if the readers have IRQs disabled, so must the
     grace-period wait

  Miscellaneous updates:
   - Update stallwarn.rst documentation for the re-implementation of RCU
     Tasks Trace in terms of SRCU
   - Fix the lazy-callback shrink scanner budget computation so that it
     honors the reclaim budget
   - Avoid panicking on RCU CPU stalls that end before the warning can
     be printed
   - Add "running" and "boosted" indications to the RCU task stall
     warning output
   - People have been (incorrectly) relying on rcu_barrier() to wait for
     kfree_rcu() callbacks and processing. But it turns out to be easier
     to fix rcu_barrier() to meet their expectations than to fix their
     code to live within the earlier rcu_barrier() specification. So
     rcu_barrier() now waits on kfree_rcu() callbacks and processing
   - Disable RCU Tasks console output that track when this RCU flavor
     switches between per-CPU and global callback queuing. New use cases
     appeared that generated enough console traffic to cause trouble,
     and no one seemed to care about these messages. For those needing
     those messages, there is a new rcupdate.rcu_task_collapse_debug
     kernel boot parameter
   - Fix __rcu pointer attribute handling to eliminate false positives
   - Fix typos and drop redundant #include directives"

* tag 'rcu.2026.10.12b' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (46 commits)
  rcutorture: Add atomic SRCU cross-CPU IRQ context mismatch test
  selftests/rcutorture: Fix double nerrs count in srcu_lockdep.sh
  selftests/rcutorture: Wire atomic SRCU into srcu_lockdep.sh
  rcutorture: Add atomic SRCU lockdep support
  rcutorture: Fix kvm-again.sh re-run failure on ppc64
  torture:  Allow specifying alternative ssh command to kvm-remote.sh
  rcutorture: Synchronously wait for all rcu_torture_irq() callbacks to complete
  rcutorture: Fix divide-by-zero with fwd_progress_div=1
  srcutree: Preserve IRQ state in synchronize_srcu_atomic() callchain
  srcutiny: Add lockdep and early-boot checks to synchronize_srcu_atomic()
  srcutree: Add lockdep and early-boot checks to synchronize_srcu_atomic()
  srcutree: Skip torture to-big transition for atomic SRCU
  srcutree: Don't transition atomic SRCU to big in srcu_gp_end()
  srcutree: Make init_srcu_struct_atomic() prevent transition to big
  srcu: Restrict atomic-SRCU non_block annotation to task context
  srcutree: Remove srcu_barrier() sleep for atomic SRCU
  srcutree: Skip callback scheduling for atomic SRCU grace periods
  srcutree: Add reader-free fastpath to synchronize_srcu_atomic()
  rcutorture: Add atomic-SRCU support to torture.sh
  srcutree: Explicitly note DEFINE_SRCU() needs for srcu_barrier()
  ...
2026-10-21 10:04:13 -10:00
arch Merge __{get,put}_user() removal branch 2026-10-21 07:19:30 -10:00
block vfs-7.4-rc1.iomap 2026-10-19 18:33:02 -10:00
certs treewide: fix indentation and whitespace in Kconfig files 2026-05-28 21:24:42 -07:00
crypto lib/crypto: sparc/aes-xts: Add optimization using the AES opcodes 2026-10-04 21:40:47 +02:00
Documentation RCU updates: 2026-10-21 10:04:13 -10:00
drivers Merge __{get,put}_user() removal branch 2026-10-21 07:19:30 -10:00
fs lsm/stable-7.4 PR 20261016 2026-10-20 20:04:07 -10:00
include RCU updates: 2026-10-21 10:04:13 -10:00
init lsm/stable-7.4 PR 20261016 2026-10-20 20:04:07 -10:00
io_uring vfs-7.4-rc1.file 2026-10-19 17:35:50 -10:00
ipc vfs-7.4-rc1.idmap 2026-10-19 17:57:49 -10:00
kernel RCU updates: 2026-10-21 10:04:13 -10:00
lib bitmap updates for v7.4 2026-10-21 09:49:47 -10:00
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 \n 2026-10-20 16:30:13 -10:00
net Merge __{get,put}_user() removal branch 2026-10-21 07:19:30 -10:00
rust bitmap updates for v7.4 2026-10-21 09:49:47 -10:00
samples configfs: Updates for v7.4 2026-10-20 16:25:43 -10:00
scripts It was a reasonably busy cycle for docs; changes include: 2026-10-20 14:38:38 -10:00
security lsm/stable-7.4 PR 20261016 2026-10-20 20:04:07 -10:00
sound ASoC: amd: yc: disable MSI on resume 2026-10-13 14:32:22 +01:00
tools RCU updates: 2026-10-21 10:04:13 -10:00
usr usr: Correct a spelling by changing a letter 2026-08-05 14:51:58 +02:00
virt vfs-7.4-rc1.idmap 2026-10-19 17:57:49 -10:00
.clang-format drm/bridge: rename drm_for_each_bridge_in_chain_scoped() to drm_for_each_bridge_in_chain() 2026-07-14 17:55:51 +02:00
.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 2026-09-07 10:01:33 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore SPDX patches for 7.2-rc1 2026-06-22 12:06:22 -07:00
.mailmap Changes since last update: 2026-10-20 16:50:37 -10:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml
AGENTS.md docs: add AGENTS.md as a symlink to README 2026-10-14 11:45:46 -06:00
COPYING
CREDITS vfs-7.4-rc1.bfs 2026-10-19 16:55:31 -10:00
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 bitmap updates for v7.4 2026-10-21 09:49:47 -10:00
Makefile It was a reasonably busy cycle for docs; changes include: 2026-10-20 14:38:38 -10:00
README README: remove out of place emdashes 2026-07-15 10:51:29 -06:00

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