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 tracefs fixes from Steven Rostedt:
- Use list_add_tail_rcu() for walking eventfs children
The linked list of children is protected by SRCU and list walkers can
walk the list with only using SRCU. Using just list_add_tail() on
weakly ordered architectures can cause issues. Instead use
list_add_tail_rcu().
- Hold eventfs_mutex and SRCU for remount walk events
The trace_apply_options() walks the tracefs_inodes where some are
eventfs inodes and eventfs_remount() is called which in turn calls
eventfs_set_attr(). This walk only holds normal RCU read locks, but
the eventfs_mutex and SRCU should be held.
Add a eventfs_remount_(un)lock() helpers to take the necessary locks
before iterating the list.
* tag 'tracefs-v7.1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
eventfs: Hold eventfs_mutex and SRCU when remount walks events
eventfs: Use list_add_tail_rcu() for SRCU-protected children list
Pull ktest updates from Steven Rostedt:
- Fix month in date timestamp used to create failure directories
On failure, a directory is created to store the logs and config file
to analyze the failure. The Perl function localtime is used to create
the data timestamp of the directory. The month passed back from that
function starts at 0 and not 1, but the timestamp used does not
account for that. Thus for April 20, 2026, the timestamp of 20260320
is used, instead of 20260420.
- Save the logfile to the failure directory
Just the test log was saved to the directory on failure, but there's
useful information in the full logfile that can be helpful to
analyzing the failure. Save the logfile as well.
* tag 'ktest-v7.1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-ktest:
ktest: Add logfile to failure directory
ktest: Fix the month in the name of the failure directory
Commit 340f0c7067a9 ("eventfs: Update all the eventfs_inodes from the
events descriptor") had eventfs_set_attrs() recurse through ei->children
on remount. The walk only holds the rcu_read_lock() taken by
tracefs_apply_options() over tracefs_inodes, which is wrong:
- list_for_each_entry over ei->children races with the list_del_rcu()
in eventfs_remove_rec() -- LIST_POISON1 deref, same shape as
d2603279c7d6.
- eventfs_inodes are freed via call_srcu(&eventfs_srcu, ...).
rcu_read_lock() does not extend an SRCU grace period, so ti->private
can be reclaimed under the walk.
- The writes to ei->attr race with eventfs_set_attr(), which holds
eventfs_mutex.
Reproducer:
while :; do mount -o remount,uid=$((RANDOM%1000)) /sys/kernel/tracing; done &
while :; do
echo "p:kp submit_bio" > /sys/kernel/tracing/kprobe_events
echo > /sys/kernel/tracing/kprobe_events
done
Wrap the events portion of tracefs_apply_options() in
eventfs_remount_lock()/_unlock() that take eventfs_mutex and
srcu_read_lock(&eventfs_srcu). eventfs_set_attrs() doesn't sleep so the
nested rcu_read_lock() is fine; lockdep_assert_held() pins the contract.
Comment in tracefs_drop_inode() said "RCU cycle" -- it is SRCU.
Fixes: 340f0c7067a9 ("eventfs: Update all the eventfs_inodes from the events descriptor")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260418191737.10289-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Pull ring-buffer fix from Steven Rostedt:
- Make undefsyms_base.c into a real file
The file undefsyms_base.c is used to catch any symbols used by a
remote ring buffer that is made for use of a pKVM hypervisor. As it
doesn't share the same text as the rest of the kernel, referencing
any symbols within the kernel will make it fail to be built for the
standalone hypervisor.
A file was created by the Makefile that checked for any symbols that
could cause issues. There's no reason to have this file created by
the Makefile, just create it as a normal file instead.
* tag 'trace-ring-buffer-v7.1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: Make undefsyms_base.c a first-class citizen
The logfile contains a lot of useful information about the tests being
run. Add it to the stored failure directory when the test fails.
Cc: John 'Warthog9' Hawley <warthog9@kernel.org>
Link: https://patch.msgid.link/20260420142315.7bbc3624@fedora
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Commit d2603279c7d6 ("eventfs: Use list_del_rcu() for SRCU protected
list variable") converted the removal side to pair with the
list_for_each_entry_srcu() walker in eventfs_iterate(). The insertion
in eventfs_create_dir() was left as a plain list_add_tail(), which on
weakly-ordered architectures can expose a new entry to the SRCU reader
before its list pointers and fields are observable.
Use list_add_tail_rcu() so the publication pairs with the existing
list_del_rcu() and list_for_each_entry_srcu().
Fixes: 43aa6f97c2d0 ("eventfs: Get rid of dentry pointers without refcounts")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260418152251.199343-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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()
Linus points out that dumping undefsyms_base.c form the Makefile
is rather ugly, and that a much better course of action would be
to have this file as a first-class citizen in the git tree.
This allows some extra cleanup in the Makefile, and the removal of
the .gitignore file in kernel/trace.
Cc: Marc Zyngier <maz@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/CAHk-=wieqGd_XKpu8UxDoyADZx8TDe8CF3RmkUXt5N_9t5Pf_w@mail.gmail.com
Link: https://lore.kernel.org/all/20260421095446.2951646-1-maz@kernel.org/
Link: https://patch.msgid.link/20260421100455.324333-1-pbonzini@redhat.com
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
The Perl localtime() function returns the month starting at 0 not 1. This
caused the date produced to create the directory for saving files of a
failed run to have the month off by one.
machine-test-useconfig-fail-20260314073628
The above happened in April, not March. The correct name should have been:
machine-test-useconfig-fail-20260414073628
This was somewhat confusing.
Cc: stable@vger.kernel.org
Cc: John 'Warthog9' Hawley <warthog9@kernel.org>
Link: https://patch.msgid.link/20260420142426.33ad0293@fedora
Fixes: 7faafbd69639b ("ktest: Add open and close console and start stop monitor")
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Moving to guard() usage removed the need of using the 'ret' variable but
it wasn't removed. As it was set to zero, the compiler in use didn't warn
(although some compilers do).
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260414110344.75c0663f@robin
Fixes: 4d9b262031f ("eventfs: Simplify code using guard()s")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202604100111.AAlbQKmK-lkp@intel.com/
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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>
This odd file was added to automatically figure out tool-generated
symbols.
Honestly, it *should* have been just a real honest-to-goodness regular
file in git, instead of having strange code to generate it in the
Makefile, but that is not how that silly thing works. So now we need to
ignore it explicitly.
Fixes: 1211907ac0b5 ("tracing: Generate undef symbols allowlist for simple_ring_buffer")
Cc: Vincent Donnefort <vdonnefort@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
STORE_FAILURES was only saved from fail(), so paths that reached dodie()
could exit without preserving failure logs.
That includes fatal hook paths such as:
POST_BUILD_DIE = 1
and ordinary failures when:
DIE_ON_FAILURE = 1
Call save_logs("fail", ...) from dodie() too so fatal failures keep the
same STORE_FAILURES artifacts as non-fatal fail() paths.
Cc: John Hawley <warthog9@eaglescrag.net>
Link: https://patch.msgid.link/20260318-ktest-fixes-v1-1-9dd94d46d84c@suse.com
Signed-off-by: Ricardo B. Marlière <rbm@suse.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Commit e4d32142d1de ("tracing: Fix tracefs mount options") moved the
option application from tracefs_fill_super() to tracefs_reconfigure()
called from tracefs_get_tree(). This fixed mount options being ignored
on user-space mounts when the superblock already exists, but introduced
a regression for the initial kernel-internal mount.
On the first mount (via simple_pin_fs during init), sget_fc() transfers
fc->s_fs_info to sb->s_fs_info and sets fc->s_fs_info to NULL. When
tracefs_get_tree() then calls tracefs_reconfigure(), it sees a NULL
fc->s_fs_info and returns early without applying any options. The root
inode keeps mode 0755 from simple_fill_super() instead of the intended
TRACEFS_DEFAULT_MODE (0700).
Furthermore, even on subsequent user-space mounts without an explicit
mode= option, tracefs_apply_options(sb, true) gates the mode behind
fsi->opts & BIT(Opt_mode), which is unset for the defaults. So the
mode is never corrected unless the user explicitly passes mode=0700.
Restore the tracefs_apply_options(sb, false) call in tracefs_fill_super()
to apply default permissions on initial superblock creation, matching
what debugfs does in debugfs_fill_super().
Cc: stable@vger.kernel.org
Fixes: e4d32142d1de ("tracing: Fix tracefs mount options")
Link: https://patch.msgid.link/20260404134747.98867-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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
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