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Mikhail Gavrilov 7cbaa0f457 entry: Account the deferred hrtimer rearm as hardirq context for lockdep
On a desktop debug kernel (PROVE_LOCKING, KASAN, LOCKDEP_CHAINS_BITS=19)
lockdep switches itself off after about two days of uptime with
"BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!", and locking is not validated
until the next reboot. In the last such boot the pool ran out after 46.6
hours, and a fifth of it, 533509 of 2621431 chain hlocks in 63838 of
344717 chains, had been created by the deferred hrtimer rearm on return
from interrupt.

Make lockdep account that rearm as part of the timer interrupt it
belongs to.

Commit 15dd3a9488
("hrtimer: Push reprogramming timers into the interrupt return path")
moved the reprogramming of the clock event device out of the timer
interrupt into the interrupt return path. On return to kernel mode
irqentry_exit_to_kernel_mode_after_preempt() performs it after
irq_exit_rcu() has already left lockdep's hardirq context. lockdep
therefore records hrtimer_bases.lock and the timekeeper sequence count
as taken by the interrupted context, on top of the locks that context
holds, and every distinct held-lock stack an interrupt hits adds two
lock chains. When the rearm runs from irq_enter_rcu() or
__irq_exit_rcu() it is still inside lockdep's hardirq context, and there
the same acquisitions reuse one pair of chains.

The dependencies recorded on the return path are "lock held with
interrupts enabled -> hrtimer_bases.lock". Such a lock is hardirq-unsafe
and hrtimer_bases.lock is hardirq-safe, so a path in the reverse
direction is already reported by the irq-safety checks without these
edges.

Re-enter lockdep's hardirq context around the rearm on the kernel return
path. The return to user mode path holds no locks and is left alone, as
is the rearm in __schedule(), which runs under the runqueue lock.

With the same kernel tree, configuration and workload, one hour of
uptime including a full kernel build, the chains of this shape, with
hrtimer_bases.lock and optionally the timekeeper sequence count on top
of a held-lock stack outside the scheduler, go from 13266 (96187 chain
hlocks, 15.9% of those in use) to 4. Those 4 come from clock_was_set(),
which takes cpus_read_lock() and each CPU's hrtimer_bases.lock and reads
the clock under it.

Fixes: 15dd3a9488 ("hrtimer: Push reprogramming timers into the interrupt return path")
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20261013071318.33300-1-mikhail.v.gavrilov@gmail.com
2026-10-14 15:11:48 +02:00
arch x86 fix: 2026-10-11 08:23:06 -07:00
block block-7.3-20261002 2026-10-02 12:25:40 -07:00
certs treewide: fix indentation and whitespace in Kconfig files 2026-05-28 21:24:42 -07:00
crypto crypto: aes - Fix undesired override of some optimized AES modes 2026-09-30 08:38:06 -07:00
Documentation spi: Fixes for v7.3 2026-10-11 11:33:26 -07:00
drivers spi: Fixes for v7.3 2026-10-11 11:33:26 -07:00
fs xfs: fix exchange-range-to-eof file size exchange 2026-10-11 08:23:43 +02:00
include entry: Account the deferred hrtimer rearm as hardirq context for lockdep 2026-10-14 15:11:48 +02:00
init Random number generator fixes for Linux 7.3-rc6. 2026-10-02 11:28:45 -07:00
io_uring io_uring-7.3-20261010 2026-10-11 08:53:11 -07:00
ipc mm.git review status for master..mm-nonmm-stable 2026-08-23 08:07:11 -07:00
kernel futex: Fix mm reuse handling for FUT_OFF_MMSHARED 2026-10-14 15:11:48 +02:00
lib lib/dim: add KUnit test for dim_calc_stats() 2026-10-02 07:52:31 +01:00
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 mm: don't schedule deferred kernel page table freeing while booting 2026-10-06 16:44:18 -07:00
net vsock: Fix memory leak in vmci_transport_recv_dgram_cb() 2026-10-08 11:46:13 -07:00
rust rust: net: netlink: validate attribute length before casting to c_int 2026-09-29 12:28:03 +02:00
samples rust: samples: add missing newlines in rust_print_main 2026-09-01 02:20:22 +02:00
scripts hid-for-linus-2026092202 2026-09-22 10:30:17 -07:00
security Landlock fix for v7.3-rc7 2026-10-11 11:49:08 -07:00
sound ASoC: Fixes for v7.3 2026-10-08 10:49:55 +02:00
tools vfs-7.3-rc7.fixes 2026-10-09 23:37:44 +02:00
usr usr: Correct a spelling by changing a letter 2026-08-05 14:51:58 +02:00
virt KVM: WARN if vCPU creation is in-progress when locking all vCPUs 2026-09-26 00:49:49 -04:00
.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 7 hotfixes. 4 are cc:stable. 2026-10-08 12:35:20 +02:00
.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 COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Driver core fixes for 7.3-rc2 2026-09-05 11:59:05 -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 Mark the ext4 data=journal feature as being deprecated and will be 2026-10-08 17:37:49 +02:00
Makefile Linux 7.3-rc7 2026-10-11 20:04:55 -07:00
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