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 regulator fix from Mark Brown:
"A fix from Arnd re-adding a dependency on gpiolib which was implicitly
pulled in via an OF specific route which got removed as part of a
cleanup"
* tag 'regulator-fix-v7.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator:
regulator: rpi-panel-attiny: add back GPIOLIB dependency
Pull regmap fix from Mark Brown:
"A fix from Colin for a spelling mistake in a dev_warn() message"
* tag 'regmap-v7.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/broonie/regmap:
regmap: sdw-mbq: Fix spelling mistake "undeferable" -> "undeferrable"
This driver provides a gpio chip, which is only possible when GPIOLIB
is enabled, which was previously guaranteed by the CONFIG_OF_GPIO
dependency that is now gone:
ERROR: modpost: "gpiochip_get_data" [drivers/regulator/rpi-panel-attiny-regulator.ko] undefined!
ERROR: modpost: "devm_gpiochip_add_data_with_key" [drivers/regulator/rpi-panel-attiny-regulator.ko] undefined!
Add an explicit GPIOLIB dependency instead.
Fixes: bf017304fce1 ("regulator: drop unneeded dependencies on OF_GPIO")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20260429135812.112514-1-arnd@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Pull MM fixes from Andrew Morton:
"20 hotfixes. All are for MM (and for MMish maintainers). 9 are
cc:stable and the remainder are for post-7.0 issues or aren't deemed
suitable for backporting.
There are two DAMON series from SeongJae Park which address races
which could lead to use-after-free errors, and avoid the possibility
of presenting stale parameter values to users"
* tag 'mm-hotfixes-stable-2026-04-30-15-39' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm:
mm: memcontrol: fix rcu unbalance in get_non_dying_memcg_end()
mm/userfaultfd: detect VMA type change after copy retry in mfill_copy_folio_retry()
MAINTAINERS: remove stale kdump project URL
mm/damon/stat: detect and use fresh enabled value
mm/damon/lru_sort: detect and use fresh enabled and kdamond_pid values
mm/damon/reclaim: detect and use fresh enabled and kdamond_pid values
selftests/mm: specify requirement for PROC_MEM_ALWAYS_FORCE=y
mm/damon/sysfs-schemes: protect path kfree() with damon_sysfs_lock
mm/damon/sysfs-schemes: protect memcg_path kfree() with damon_sysfs_lock
MAINTAINERS: update Li Wang's email address
MAINTAINERS, mailmap: update email address for Qi Zheng
MAINTAINERS: update Liam's email address
mm/hugetlb_cma: round up per_node before logging it
MAINTAINERS: fix regex pattern in CORE MM category
mm/vma: do not try to unmap a VMA if mmap_prepare() invoked from mmap()
mm: start background writeback based on per-wb threshold for strictlimit BDIs
kho: fix error handling in kho_add_subtree()
liveupdate: fix return value on session allocation failure
mailmap: update entry for Dan Carpenter
vmalloc: fix buffer overflow in vrealloc_node_align()
There is a spelling mistake in a dev_warn message. Fix it.
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://patch.msgid.link/20260424112425.32129-1-colin.i.king@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Pull mtd fixes from Miquel Raynal:
"Besides an out-of-bound bug, this is about properly supporting Winbond
octal SPI NAND chips which use a specific pattern for stuffing more
address bits in some operations. This uses the spi-mem flag in SPI
NAND that was added to the spi-mem layer just before the merge window
through the spi tree"
* tag 'mtd/fixes-for-7.1-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux:
mtd: spinand: winbond: Fix ODTR write VCR on W35NxxJW
mtd: spinand: winbond: Set the packed page read flag to W35N02/04JW
mtd: spinand: Add support for packed read data ODTR commands
mtd: spi-nor: debugfs: fix out-of-bounds read in spi_nor_params_show()
Currently, get_non_dying_memcg_start() and get_non_dying_memcg_end() both
evaluate cgroup_subsys_on_dfl(memory_cgrp_subsys) independently to
determine whether to acquire or release the RCU read lock.
However, the result of cgroup_subsys_on_dfl() can change dynamically at
runtime due to cgroup hierarchy rebinding (e.g., when the memory
controller is moved between cgroup v1 and v2 hierarchies). This can cause
the following warning:
=====================================
WARNING: bad unlock balance detected!
7.0.0-next-20260420+ #83 Tainted: G W
-------------------------------------
memcg-repro/270 is trying to release lock (rcu_read_lock) at:
[<ffffffff815f57f7>] rcu_read_unlock+0x17/0x60
but there are no more locks to release!
other info that might help us debug this:
1 lock held by memcg-repro/270:
#0: ffff888102fa2088 (vm_lock){++++}-{0:0}, at: do_user_addr_fault+0x285/0x880
stack backtrace:
CPU: 0 UID: 0 PID: 270 Comm: memcg-repro Tainted: G W 7.0.0-next-20260420+ #
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
Call Trace:
<TASK>
? rcu_read_unlock+0x17/0x60
dump_stack_lvl+0x77/0xb0
print_unlock_imbalance_bug+0xe0/0xf0
? rcu_read_unlock+0x17/0x60
lock_release+0x21d/0x2a0
rcu_read_unlock+0x1c/0x60
do_pte_missing+0x233/0xb40
__handle_mm_fault+0x80e/0xcd0
handle_mm_fault+0x146/0x310
do_user_addr_fault+0x303/0x880
exc_page_fault+0x9b/0x270
asm_exc_page_fault+0x26/0x30
RIP: 0033:0x5590e4eb41ea
Code: 61 cc 66 0f 6f e0 66 0f 61 c2 66 0f db cd 66 0f 69 e2 66 0f 6f d0 66 0f 69 d4 66 0f 61 0
RSP: 002b:00007ffcad25f030 EFLAGS: 00010202
RAX: 00005590e4eb8010 RBX: 00007ffcad260f7d RCX: 00007f73c474d44d
RDX: 00005590e4eb80a0 RSI: 00005590e4eb503c RDI: 000000000000000f
RBP: 00005590e4eb70a0 R08: 0000000000000000 R09: 00007f73c483a680
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffcad25f180 R14: 00005590e4eb6dd8 R15: 00007f73c4869020
</TASK>
------------[ cut here ]------------
Fix this by explicitly tracking the RCU lock state, ensuring that
rcu_read_unlock() in get_non_dying_memcg_end() is strictly paired with the
lock acquisition, regardless of any runtime rebinding events.
Link: https://lore.kernel.org/20260429073105.44472-1-qi.zheng@linux.dev
Fixes: 8285917d6f38 ("mm: memcontrol: prepare for reparenting non-hierarchical stats")
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Pull clk fix from Stephen Boyd:
"One more fix for the merge window to avoid a boot hang on
Raspberry Pi 3B by marking the VEC clk critical so that it
doesn't get turned off and hang the bus"
* tag 'clk-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux:
clk: bcm: rpi: Mark VEC clock as CLK_IGNORE_UNUSED
Pull ACPI support fixes from Rafael Wysocki:
"These fix leftover issues in the ACPI Time and Alarm Device (TAD)
driver on top of the recently merged updates of it and address
assorted issues in the ACPI support code:
- Fix removal code ordering in the ACPI TAD driver, refine timer
value computations and checks in its RTC class device interface,
make it use the __ATTRIBUTE_GROUPS() macro, and fix a comment in it
(Rafael Wysocki)
- Fix EINJV2 memory error injection in APEI (Tony Luck)
- Add missing notifier_block structure forward declaration to
acpi_bus.h (Bartosz Golaszewski)
- Fix related_cpus inconsistency during CPU hotplug in the ACPI CPPC
library (Jinjie Ruan)
- Add a quirk to force native backlight on HP OMEN 16 (8A44) in the
ACPI video bus driver (Shivam Kalra)"
* tag 'acpi-7.1-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
ACPI: bus: add missing forward declaration to acpi_bus.h
ACPI: video: force native backlight on HP OMEN 16 (8A44)
ACPI: TAD: Fix up a comment in acpi_tad_probe()
ACPI: TAD: RTC: Refine timer value computations and checks
ACPI: TAD: Use devres for all driver cleanup
ACPI: TAD: Use __ATTRIBUTE_GROUPS() macro
ACPI: CPPC: Fix related_cpus inconsistency during CPU hotplug
ACPI: APEI: EINJ: Fix EINJV2 memory error injection
ACPICA: Provide #defines for EINJV2 error types
In most scenarios this variant is actually unused (VCR is written in
SSDR mode), but we need to provide an octal variant. The address is 24
bits but is sent over 4 bytes MSB first. This means we need to shift the
register address by one extra byte for the address to be correct.
I didn't catch this initially because the volatile register region is
256 bytes wide, so the write-then-read procedure did work with the small
register addresses I was using at that time: 0 and 1.
Fixes: 44a2f49b9bdc ("mtd: spinand: winbond: W35N octal DTR support")
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
mfill_copy_folio_retry() drops mmap_lock for the copy_from_user() call.
During this window, the VMA can be replaced with a different type (e.g.
hugetlb), making the caller's ops pointer stale. Subsequent use of the
stale ops would dispatch into the wrong per-vma handlers.
Capture the VMA's ops via vma_uffd_ops() before dropping the lock and
compare against the current vma_uffd_ops() after re-acquiring it.
Return -EAGAIN if they differ so the operation can be retried. This
avoids comparing against the caller's ops which may have been
overridden to anon_uffd_ops for MAP_PRIVATE file-backed mappings.
Link: https://lore.kernel.org/20260424183638.196227-1-devnexen@gmail.com
Fixes: 6ab703034f14 ("userfaultfd: mfill_atomic(): remove retry logic")
Reported-by: Usama Arif <usama.arif@linux.dev>
Closes: https://lore.kernel.org/all/20260410114809.3592720-1-usama.arif@linux.dev/
Signed-off-by: David Carlier <devnexen@gmail.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Pull PCIe TSP update from Dan Williams:
"A small update for the TSM core. It is arguably a fix and coming in
late as I have been offline the past few weeks:
- Drop class_create() for the 'tsm' class"
* tag 'tsm-for-7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/devsec/tsm:
virt: coco: change tsm_class to a const struct
On Raspberry Pi 3B, the VEC clock is used by the VideoCore firmware
display driver, which remains active until the vc4 driver loads and
sends NOTIFY_DISPLAY_DONE. If this clock is disabled during boot, a bus
lockup happens and the firmware becomes unresponsive, causing a complete
system lockup.
Mark the VEC clock with CLK_IGNORE_UNUSED so it survives the unused
clock disablement and remains available until the vc4 driver takes over
display management.
Fixes: 672299736af6 ("clk: bcm: rpi: Manage clock rate in prepare/unprepare callbacks")
Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://lore.kernel.org/r/5f0bec08-f458-4fba-8bf3-06817a100c4c@sirena.org.uk
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Link: https://patch.msgid.link/20260401111416.562279-2-mcanal@igalia.com
Tested-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Brian Masney <bmasney@redhat.com> # Active contributor to clk
Reviewed-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Pull smb client fixes from Steve French:
- multichannel crediting fix
- memory allocation improvement for smb2_compound_op
- remove some dead code
* tag 'v7.1-rc2-smb3-client-fixes' of git://git.samba.org/sfrench/cifs-2.6:
cifs: change_conf needs to be called for session setup
smb: client: change allocation requirements in smb2_compound_op
smb/client: remove unused smb3_parse_opt()
Merge assorted ACPI support fixes for 7.1-rc2:
- Fix EINJV2 memory error injection in APEI (Tony Luck)
- Add missing notifier_block structure forward declaration to
acpi_bus.h (Bartosz Golaszewski)
- Fix related_cpus inconsistency during CPU hotplug in the ACPI CPPC
library (Jinjie Ruan)
- Add a quirk to force native backlight on HP OMEN 16 (8A44) in the
ACPI video bus driver (Shivam Kalra)
* acpi-apei:
ACPI: APEI: EINJ: Fix EINJV2 memory error injection
ACPICA: Provide #defines for EINJV2 error types
* acpi-bus:
ACPI: bus: add missing forward declaration to acpi_bus.h
* acpi-cppc:
ACPI: CPPC: Fix related_cpus inconsistency during CPU hotplug
* acpi-video:
ACPI: video: force native backlight on HP OMEN 16 (8A44)