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 kgdb update from Daniel Thompson:
"Only a very small update for kgdb this cycle: a single patch from
Kexin Sun that fixes some outdated comments"
* tag 'kgdb-7.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux:
kgdb: update outdated references to kgdb_wait()
Pull tomoyo update from Tetsuo Handa:
"Handle 64-bit inode numbers"
* tag 'tomoyo-pr-20260422' of git://git.code.sf.net/p/tomoyo/tomoyo:
tomoyo: use u64 for holding inode->i_ino value
The function kgdb_wait() was folded into the static function
kgdb_cpu_enter() by commit 62fae312197a ("kgdb: eliminate
kgdb_wait(), all cpus enter the same way"). Update the four stale
references accordingly:
- include/linux/kgdb.h and arch/x86/kernel/kgdb.c: the
kgdb_roundup_cpus() kdoc describes what other CPUs are rounded up
to call. Because kgdb_cpu_enter() is static, the correct public
entry point is kgdb_handle_exception(); also fix a pre-existing
grammar error ("get them be" -> "get them into") and reflow the
text.
- kernel/debug/debug_core.c: replace with the generic description
"the debug trap handler", since the actual entry path is
architecture-specific.
- kernel/debug/gdbstub.c: kgdb_cpu_enter() is correct here (it
describes internal state, not a call target); add the missing
parentheses.
Suggested-by: Daniel Thompson <daniel@riscstar.com>
Assisted-by: unnamed:deepseek-v3.2 coccinelle
Signed-off-by: Kexin Sun <kexinsun@smail.nju.edu.cn>
Pull s390 updates from Vasily Gorbik:
- Add support for CONFIG_PAGE_TABLE_CHECK and enable it in
debug_defconfig. s390 can only tell user from kernel PTEs via the mm,
so mm_struct is now passed into pxx_user_accessible_page() callbacks
- Expose the PCI function UID as an arch-specific slot attribute in
sysfs so a function can be identified by its user-defined id while
still in standby. Introduces a generic ARCH_PCI_SLOT_GROUPS hook in
drivers/pci/slot.c
- Refresh s390 PCI documentation to reflect current behavior and cover
previously undocumented sysfs attributes
- zcrypt device driver cleanup series: consistent field types, clearer
variable naming, a kernel-doc warning fix, and a comment explaining
the intentional synchronize_rcu() in pkey_handler_register()
- Provide an s390 arch_raw_cpu_ptr() that avoids the detour via
get_lowcore() using alternatives, shrinking defconfig by ~27 kB
- Guard identity-base randomization with kaslr_enabled() so nokaslr
keeps the identity mapping at 0 even with RANDOMIZE_IDENTITY_BASE=y
- Build S390_MODULES_SANITY_TEST as a module only by requiring KUNIT &&
m, since built-in would not exercise module loading
- Remove the permanently commented-out HMCDRV_DEV_CLASS create_class()
code in the hmcdrv driver
- Drop stale ident_map_size extern conflicting with asm/page.h
* tag 's390-7.1-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux:
s390/zcrypt: Fix warning about wrong kernel doc comment
PCI: s390: Expose the UID as an arch specific PCI slot attribute
docs: s390/pci: Improve and update PCI documentation
s390/pkey: Add comment about synchronize_rcu() to pkey base
s390/hmcdrv: Remove commented out code
s390/zcrypt: Slight rework on the agent_id field
s390/zcrypt: Explicitly use a card variable in _zcrypt_send_cprb
s390/zcrypt: Rework MKVP fields and handling
s390/zcrypt: Make apfs a real unsigned int field
s390/zcrypt: Rework domain processing within zcrypt device driver
s390/zcrypt: Move inline function rng_type6cprb_msgx from header to code
s390/percpu: Provide arch_raw_cpu_ptr()
s390: Enable page table check for debug_defconfig
s390/pgtable: Add s390 support for page table check
s390/pgtable: Use set_pmd_bit() to invalidate PMD entry
mm/page_table_check: Pass mm_struct to pxx_user_accessible_page()
s390/boot: Respect kaslr_enabled() for identity randomization
s390/Kconfig: Make modules sanity test a module-only option
s390/setup: Drop stale ident_map_size declaration
TOMOYO is treating numeric fields (including inode->i_ino) as "unsigned
long". Now that commit 0b2600f81cef ("treewide: change inode->i_ino from
unsigned long to u64") went upstream, update affected portions in TOMOYO.
While an administrator might write a rule that compares inode->i_ino with
an immediate value, this patch changes type of variable for inode->i_ino
to "u64" but does not change type of variable for the corresponding
immediate value to "u64" due to the following reasons.
It is likely that rules that compare inode->i_ino are for testing whether
the directories involved in e.g. rename() operation are the same (i.e.
comparison between two inode->i_ino values rather than one inode->i_ino
value and one immediate value).
It unlikely makes sense to compare inode->i_ino with an immediate value
larger than UINT_MAX.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Pull Hyper-V updates from Wei Liu:
- Fix cross-compilation for hv tools (Aditya Garg)
- Fix vmemmap_shift exceeding MAX_FOLIO_ORDER in mshv_vtl (Naman Jain)
- Limit channel interrupt scan to relid high water mark (Michael
Kelley)
- Export hv_vmbus_exists() and use it in pci-hyperv (Dexuan Cui)
- Fix cleanup and shutdown issues for MSHV (Jork Loeser)
- Introduce more tracing support for MSHV (Stanislav Kinsburskii)
* tag 'hyperv-next-signed-20260421' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux:
x86/hyperv: Skip LP/VP creation on kexec
x86/hyperv: move stimer cleanup to hv_machine_shutdown()
Drivers: hv: vmbus: fix hyperv_cpuhp_online variable shadowing
mshv: Add tracepoint for GPA intercept handling
mshv_vtl: Fix vmemmap_shift exceeding MAX_FOLIO_ORDER
tools: hv: Fix cross-compilation
Drivers: hv: vmbus: Export hv_vmbus_exists() and use it in pci-hyperv
mshv: Introduce tracing support
Drivers: hv: vmbus: Limit channel interrupt scan to relid high water mark
Fix this warning:
Warning: drivers/s390/crypto/zcrypt_msgtype6.c:1253 This comment
starts with '/**', but isn't a kernel-doc comment. Refer to
Documentation/doc-guide/kernel-doc.rst
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202603252022.vEojGo3V-lkp@intel.com/
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Pull EDAC fix from Borislav Petkov:
- Fix the error path ordering when the driver-private descriptor
allocation fails
* tag 'edac_urgent_for_7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/ras/ras:
EDAC/mc: Fix error path ordering in edac_mc_alloc()
Pull probes fixes from Masami Hiramatsu:
"fprobe bug fixes:
- Prevent re-registration
Add an earlier check to reject re-registering an already active
fprobe before its state is modified during the initialization phase
- Robustness in failure paths:
- Ensure fprobes are correctly removed from all internal tables
and properly RCU-freed during registration failure
- Make unregister_fprobe() proceed with unregistration even if
temporary memory allocation fails
- RCU safety in module unloading
Avoid a potential "sleep in RCU" warning by removing a kcalloc()
call in the module notifier path. This also tries to remove
fprobe_hash_node even if memory allocation fails.
- Type-aware unregistration
Fix a bug where unregistering an fprobe did not account for
different types (entry-only vs entry-exit) at the same address,
which previously left "junk" entries in the underlying
ftrace/fgraph ops
- Unregistration of empty ftrace_ops
Avoid unneeded performance overhead due to making registered
ftrace_ops empty - which means 'trace all functions'. This counts
remaining entries and unregister ftrace_ops when it becomes empty.
Two new selftests to check above fixes:
- Module Unloading Test:
Specifically verifies that fprobe events on a module are correctly
cleaned up and do not trigger 'trace-all' behavior when the module
is removed.
- Multiple Fprobe Events Test:
Ensure that having multiple fprobes on the same function correctly
manages the ftrace hash map during removal"
* tag 'probes-v7.1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
selftests/ftrace: Add a testcase for multiple fprobe events
selftests/ftrace: Add a testcase for fprobe events on module
tracing/fprobe: Fix to unregister ftrace_ops if it is empty on module unloading
tracing/fprobe: Check the same type fprobe on table as the unregistered one
tracing/fprobe: Avoid kcalloc() in rcu_read_lock section
tracing/fprobe: Remove fprobe from hash in failure path
tracing/fprobe: Unregister fprobe even if memory allocation fails
tracing/fprobe: Reject registration of a registered fprobe before init
After a kexec the logical processors and virtual processors already
exist in the hypervisor because they were created by the previous
kernel. Attempting to add them again causes either a BUG_ON or
corrupted VP state leading to MCEs in the new kernel.
Add hv_lp_exists() to probe whether an LP is already present by
calling HVCALL_GET_LOGICAL_PROCESSOR_RUN_TIME. When it succeeds the
LP exists and we skip the add-LP and create-VP loops entirely.
Also add hv_call_notify_all_processors_started() which informs the
hypervisor that all processors are online. This is required after
adding LPs (fresh boot) and is a no-op on kexec since we skip that
path.
Co-developed-by: Anirudh Rayabharam <anrayabh@linux.microsoft.com>
Signed-off-by: Anirudh Rayabharam <anrayabh@linux.microsoft.com>
Co-developed-by: Stanislav Kinsburskii <stanislav.kinsburskii@gmail.com>
Signed-off-by: Stanislav Kinsburskii <stanislav.kinsburskii@gmail.com>
Co-developed-by: Mukesh Rathor <mrathor@linux.microsoft.com>
Signed-off-by: Mukesh Rathor <mrathor@linux.microsoft.com>
Signed-off-by: Jork Loeser <jloeser@linux.microsoft.com>
Reviewed-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
On s390, an individual PCI function can generally be identified by two
identifiers, the FID and the UID. Which identifier is used depends on
the scope and the platform configuration.
The first identifier, the FID, is always available and identifies a PCI
device uniquely within a machine. The FID may be virtualized by
hypervisors, but on the LPAR level, the machine scope makes it
impossible to create the same configuration based on FIDs on two
different LPARs of the same machine, and difficult to reuse across
machines.
Such matching LPAR configurations are useful, though, allowing
standardized setups and booting a Linux installation on different LPARs.
To this end the UID, or user-defined identifier, was introduced. While
it is only guaranteed to be unique within an LPAR and only if indicated
by firmware, it allows users to replicate PCI device setups.
On s390, which uses a machine hypervisor, a per PCI function hotplug
model is used. The shortcoming with the UID then is, that it is not
visible to the user without first attaching the PCI function and
accessing the "uid" device attribute. The FID, on the other hand, is
used as the slot name and is thus known even with the PCI function in
standby.
Remedy this shortcoming by providing the UID as an attribute on the slot
allowing the user to identify a PCI function based on the UID without
having to first attach it. Do this via a macro mechanism analogous to
what was introduced by commit 265baca69a07 ("s390/pci: Stop usurping
pdev->dev.groups") for the PCI device attributes.
Reviewed-by: Gerd Bayer <gbayer@linux.ibm.com>
Reviewed-by: Julian Ruess <julianr@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com> # drivers/pci/slot.c
Link: https://lore.kernel.org/r/20260407-uid_slot-v8-2-15ae4409d2ce@linux.ibm.com
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Pull workqueue fix from Tejun Heo:
"This is a fix for a stall which triggers on ordered workqueues when
there are multiple inactive work items during workqueue property
changes through sysfs, which doesn't happen that frequently.
While really late, the fix is very low risk as it just repeats an
operation which is already being performed:
- Fix incomplete activation of multiple inactive works when
unplugging a pool_workqueue, where the pending_pwqs list
wasn't being updated for subsequent works"
* tag 'wq-for-7.0-rc7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
workqueue: Add pool_workqueue to pending_pwqs list when unplugging multiple inactive works
When the mci->pvt_info allocation in edac_mc_alloc() fails, the error path
will call put_device() which will end up calling the device's release
function.
However, the init ordering is wrong such that device_initialize() happens
*after* the failed allocation and thus the device itself and the release
function pointer are not initialized yet when they're called:
MCE: In-kernel MCE decoding enabled.
------------[ cut here ]------------
kobject: '(null)': is not initialized, yet kobject_put() is being called.
WARNING: lib/kobject.c:734 at kobject_put, CPU#22: systemd-udevd
CPU: 22 UID: 0 PID: 538 Comm: systemd-udevd Not tainted 7.0.0-rc1+ #2 PREEMPT(full)
RIP: 0010:kobject_put
Call Trace:
<TASK>
edac_mc_alloc+0xbe/0xe0 [edac_core]
amd64_edac_init+0x7a4/0xff0 [amd64_edac]
? __pfx_amd64_edac_init+0x10/0x10 [amd64_edac]
do_one_initcall
...
Reorder the calling sequence so that the device is initialized and thus the
release function pointer is properly set before it can be used.
This was found by Claude while reviewing another EDAC patch.
Fixes: 0bbb265f7089 ("EDAC/mc: Get rid of silly one-shot struct allocation in edac_mc_alloc()")
Reported-by: Claude Code:claude-opus-4.5
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Cc: stable@kernel.org
Link: https://patch.msgid.link/20260331121623.4871-1-bp@kernel.org
Pull more drm updates from Dave Airlie:
"This is a followup which is mostly next material with some fixes.
Alex pointed out I missed one of his AMD MRs from last week, so I
added that, then Jani sent the pipe reordering stuff, otherwise it's
just some minor i915 fixes and a dma-buf fix.
drm:
- Add support for AMD VSDB parsing to drm_edid
dma-buf:
- fix documentation formatting
i915:
- add support for reordered pipes to support joined pipes better
- Fix VESA backlight possible check condition
- Verify the correct plane DDB entry
amdgpu:
- Audio regression fix
- Use drm edid parser for AMD VSDB
- Misc cleanups
- VCE cs parse fixes
- VCN cs parse fixes
- RAS fixes
- Clean up and unify vram reservation handling
- GPU Partition updates
- system_wq cleanups
- Add CONFIG_GCOV_PROFILE_AMDGPU kconfig option
- SMU vram copy updates
- SMU 13/14/15 fixes
- UserQ fixes
- Replace pasid idr with an xarray
- Dither handling fix
- Enable amdgpu by default for CIK APUs
- Add IBs to devcoredump
amdkfd:
- system_wq cleanups
radeon:
- system_wq cleanups"
* tag 'drm-next-2026-04-22' of https://gitlab.freedesktop.org/drm/kernel: (62 commits)
drm/i915/display: change pipe allocation order for discrete platforms
drm/i915/wm: Verify the correct plane DDB entry
drm/i915/backlight: Fix VESA backlight possible check condition
drm/i915: Walk crtcs in pipe order
drm/i915/joiner: Make joiner "nomodeset" state copy independent of pipe order
dma-buf: fix htmldocs error for dma_buf_attach_revocable
drm/amdgpu: dump job ibs in the devcoredump
drm/amdgpu: store ib info for devcoredump
drm/amdgpu: extract amdgpu_vm_lock_by_pasid from amdgpu_vm_handle_fault
drm/amdgpu: Use amdgpu by default for CIK APUs too
drm/amd/display: Remove unused NUM_ELEMENTS macros
drm/amd/display: Replace inline NUM_ELEMENTS macro with ARRAY_SIZE
drm/amdgpu: save ring content before resetting the device
drm/amdgpu: make userq fence_drv drop explicit in queue destroy
drm/amdgpu: rework userq fence driver alloc/destroy
drm/amdgpu/userq: use dma_fence_wait_timeout without test for signalled
drm/amdgpu/userq: call dma_resv_wait_timeout without test for signalled
drm/amdgpu/userq: add the return code too in error condition
drm/amdgpu/userq: fence wait for max time in amdgpu_userq_wait_for_signal
drm/amd/display: Change dither policy for 10 bpc output back to dithering
...
Add a testcase for multiple fprobe events on the same function
so that it clears ftrace hash map correctly when removing the
events.
Link: https://lore.kernel.org/all/177669370353.132053.16801520791509406141.stgit@mhiramat.tok.corp.google.com/
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
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