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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Pull Kbuild fixes from Nicolas Schier:
- builddeb - avoid recompiles for non-cross-compiles
Avoid triggering complete rebuilds for non-cross-compile Debian
package builds by only triggering the rebuild of host tools for
actual cross-compile builds
- Never respect CONFIG_WERROR / W=e to fixdep
Avoid spurious rebuilds of fixdep w/ and w/o -Werror during a single
kbuild invocation by never respecting CONFIG_WERROR for fixdep
* tag 'kbuild-fixes-7.1-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux:
kbuild: Never respect CONFIG_WERROR / W=e to fixdep
kbuild: builddeb - avoid recompiles for non-cross-compiles
Pull power utility updates from Len Brown:
"x86_energy_perf_policy:
- Initial SoC Slider support
turbostat:
- Display HT siblings in cpu# order
- Add Module-ID column
- Print Core-ID and APIC-ID in hex
- Fix misc bugs"
* tag 'power-utilities-2026.04.25' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux:
tools/power x86_energy_perf_policy: Version 2026.04.25
tools/power x86_energy_perf_policy.8: Document SoC Slider Options
tools/power x86_energy_perf_policy: Enhances SoC Slider related checks
tools/power turbostat: v2026.04.21
tools/power turbostat: Process HT siblings in CPU order
tools/power turbostat: Show module_id column
tools/power turbostat: Print core_id and apic_id in hex
tools/power turbostat: Cleanup print helper functions
tools/power turbostat: Fix --cpu-set 1 regression on HT systems
tools/power turbostat: Fix --cpu-set 0 regression on HT systems
tools/power turbostat: Fix unrecognized option '-P'
tools/power turbostat: Fix AMD RAPL regression on big systems
tools/power/x86: Add SOC slider and platform profile support
The fixdep hostprog may be built multiple times during a single build.
Once during the configuration phase and later during the regular phase.
As only the regular build phase respects CONFIG_WERROR / W=e, the
compiler flags might change between the phases, leading to rebuilds.
Example, the rebuilds will happen twice on each invocation of the build:
$ make allyesconfig prepare
make[1]: Entering directory '/tmp/deleteme'
HOSTCC scripts/basic/fixdep
#
# No change to .config
#
HOSTCC scripts/basic/fixdep
DESCEND objtool
INSTALL libsubcmd_headers
make[1]: Leaving directory '/tmp/deleteme'
Fix the compilation flags used for scripts/basic/ before
scripts/Makefile.warn is evaluated to stop CONFIG_WERROR / W=e
influencing the fixdep build to avoid the spurious rebuilds.
Fixes: 7ded7d37e5f5 ("scripts/Makefile.extrawarn: Respect CONFIG_WERROR / W=e for hostprogs")
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20260422-kbuild-scripts-basic-werror-v1-1-8c6912ff22e0@weissschuh.net
Signed-off-by: Nicolas Schier <nsc@kernel.org>
Pull RTC updates from Alexandre Belloni:
"Subsystem:
- add data_race() in rtc_dev_poll()
Drivers:
- remove i2c_match_id usage
- abx80x: Disable alarm feature if no interrupt attached
- ti-k3: support resuming from IO DDR low power mode"
* tag 'rtc-7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/abelloni/linux:
rtc: abx80x: Disable alarm feature if no interrupt attached
rtc: ntxec: fix OF node reference imbalance
rtc: pic32: allow driver to be compiled with COMPILE_TEST
rtc: ti-k3: Add support to resume from IO DDR low power mode
rtc: cmos: Use platform_get_irq_optional() in cmos_platform_probe()
dt-bindings: rtc: add olpc,xo1-rtc to trivial-rtc
dt-bindings: rtc: sc2731: Add compatible for SC2730
rtc: add data_race() in rtc_dev_poll()
rtc: armada38x: zalloc + calloc to single allocation
dt-bindings: rtc: isl12026: convert to YAML schema
dt-bindings: rtc: microcrystal,rv3028: Allow to specify vdd-supply
rtc: max77686: convert to i2c_new_ancillary_device
dt-bindings: rtc: mpfs-rtc: permit resets
rtc: rx8025: Remove use of i2c_match_id()
rtc: rv8803: Remove use of i2c_match_id()
rtc: rs5c372: Remove use of i2c_match_id()
rtc: pcf2127: Remove use of i2c_match_id()
rtc: m41t80: Remove use of i2c_match_id()
rtc: abx80x: Remove use of i2c_match_id()
Commit e2c318225ac1 ("kbuild: deb-pkg: add
pkg.linux-upstream.nokernelheaders build profile") changed how
install-extmod-build gets called, making it always rebuild the host
programs below scripts/ if HOSTCC wasn't specified with its full triplet
on the make command line. That is, apparently, needed to fix up commit
f1d87664b82a ("kbuild: cross-compile linux-headers package when
possible") for cross-compiles. However, in the much more common case of
non-cross-compile builds this will lead to unnecessary rebuilding of
host tools including gcc plugins. This, in turn, will lead to a full
kernel rebuild on the next 'make bindeb-pkg' which is unfortunate.
Avoid that by only triggering the rebuild of host tools for actual
cross-compile builds.
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Fixes: e2c318225ac1 ("kbuild: deb-pkg: add pkg.linux-upstream.nokernelheaders build profile")
Cc: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Link: https://patch.msgid.link/20260402145116.1010901-1-minipli@grsecurity.net
Signed-off-by: Nicolas Schier <nsc@kernel.org>
Pull tpm updates from Jarkko Sakkinen:
"Here are the accumulated fixes for 7.1-rc1 and a single structural
change worth mentioning separately: Rafael's commit converting tpm_crb
from ACPI driver to a platform driver"
* tag 'for-next-tpm-7.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd:
tpm: tpm_tis: stop transmit if retries are exhausted
tpm: tpm_tis: add error logging for data transfer
tpm: avoid -Wunused-but-set-variable
tpm: Use kfree_sensitive() to free auth session in tpm_dev_release()
tpm2-sessions: Fix missing tpm_buf_destroy() in tpm2_read_public()
tpm: Fix auth session leak in tpm2_get_random() error path
tpm: i2c: atmel: fix block comment formatting
tpm_crb: Convert ACPI driver to a platform one
tpm: Make tcpci_pm_ops variable static const
Commit 795cda8338ea ("rtc: interface: Fix long-standing race when setting
alarm") exposed an issue where the rtc-abx80x driver does not clear the
alarm feature bit, but instead relies on the set_alarm operation to return
invalid.
For example, when a RTC_UIE_ON ioctl is handled, it should abort at the
feature validation. Instead, it proceeds to the rtc_timer_enqueue(),
which used to return an error from the set_alarm call. However,
following the race condition handling, which likely should not be
discarding predecing errors, a success condition is returned to the
ioctl() caller. This results in (for example):
hwclock: select() to /dev/rtc0 to wait for clock tick timed out
Notwithstanding the validity of the race condition handling, if an interrupt
wasn't specified, or could not be attached, the driver should clear the
alarm feature bit.
Fixes: 718a820a303c ("rtc: abx80x: add alarm support")
Signed-off-by: Anthony Pighin <anthony.pighin@nokia.com>
Link: https://patch.msgid.link/BN0PR08MB69510928028C933749F4139383D1A@BN0PR08MB6951.namprd08.prod.outlook.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Since v2026.02.14
Display HT siblings in cpu# order.
Add Module-ID column.
Print Core-ID and APIC-ID in hex.
Fix misc bugs.
Signed-off-by: Len Brown <len.brown@intel.com>
Since v2025.11.22:
Initial SoC Slider support
SoC Slider is an SoC-wide power/performance policy setting.
On SoC Slider systems, EPP plays a diminished role.
Whitespace cleanup via: indent -npro -kr -i8 -ts8 -sob -l160 -ss -ncs -cp1
No functional changes
Signed-off-by: Len Brown <len.brown@intel.com>
Pull fbdev fixes from Helge Deller:
- request memory region before use (cobalt_lcdfb, clps711x-fb, hgafb)
- reference cleanups in failure path (offb, savage)
- a spelling fix (atyfb)
* tag 'fbdev-for-7.1-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/linux-fbdev:
fbdev: hgafb: Request memory region before ioremap
fbdev: clps711x-fb: Request memory region for MMIO
fbdev: cobalt_lcdfb: Request memory region
fbdev: atyfb: Fix spelling mistake "enfore" -> "enforce"
fbdev: savage: fix probe-path EDID cleanup leaks
fbdev: offb: fix PCI device reference leak on probe failure
tpm_tis_send_main() will attempt to retry sending data TPM_RETRY times.
Currently, if those retries are exhausted, the driver will attempt to
call execute. The TPM will be in the wrong state, leading to the
operation simply timing out.
Instead, if there is still an error after retries are exhausted, return
that error immediately.
Cc: stable@vger.kernel.org # v6.6+
Fixes: 280db21e153d8 ("tpm_tis: Resend command to recover from data transfer errors")
Signed-off-by: Jacqueline Wong <jacqwong@google.com>
Signed-off-by: Jordan Hand <jhand@google.com>
Link: https://lore.kernel.org/r/20260415160006.2275325-3-jacqwong@google.com
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
The driver reuses the OF node of the parent multi-function device but
fails to take another reference to balance the one dropped by the
platform bus code when unbinding the MFD and deregistering the child
devices.
Fix this by using the intended helper for reusing OF nodes.
Fixes: 435af89786c6 ("rtc: New driver for RTC in Netronix embedded controller")
Cc: stable@vger.kernel.org # 5.13
Cc: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20260407122717.2676774-1-johan@kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
On large systems with HT sibling cpu#'s more than 32 apart,
HT siblings were processed and displayed in reverse order.
This was due to how set_thread_siblings() parsed the
sibling-bit-mask.
Update set_thread_siblings to instead parse the sibling-list,
like other cpu lists, and to thus order HT siblings
by ascending CPU number, no matter the size of the system.
Signed-off-by: Len Brown <len.brown@intel.com>
x86_energy_perf_policy accesses the SoC Slider via standard
user/kernel APIs to the processor_thermal_soc_slider driver.
Machines that support SoC Slider largely use it instead of EPP,
which may continue to exist in a diminished role, or vanish entirely.
Signed-off-by: Len Brown <len.brown@intel.com>