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 gfs2 updates from Andreas Gruenbacher:
- Fix possible data loss during inode evict
- Fix a race during bufdata allocation
- More careful cleaning up during a withdraw
- Prevent excessive log flushing under memory pressure
- Various other minor fixes and cleanups
* tag 'gfs2-for-7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2:
gfs2: prevent NULL pointer dereference during unmount
gfs2: hide error messages after withdraw
gfs2: wait for withdraw earlier during unmount
gfs2: inode directory consistency checks
gfs2: gfs2_log_flush withdraw fixes
gfs2: add some missing log locking
gfs2: fix address space truncation during withdraw
gfs2: drain ail under sd_log_flush_lock
gfs2: bufdata allocation race
gfs2: Remove trans_drain code duplication
gfs2: Move gfs2_remove_from_journal to log.c
gfs2: Get rid of gfs2_log_[un]lock helpers
gfs2: less aggressive low-memory log flushing
gfs2: Fix data loss during inode evict
gfs2: minor evict_[un]linked_inode cleanup
gfs2: Avoid unnecessary transactions in evict_linked_inode
gfs2: Remove unnecessary check in gfs2_evict_inode
gfs2: Call unlock_new_inode before d_instantiate
Pull fuse update from Miklos Szeredi:
- Fix possible hang in virtiofs when cleaning up a DAX inode (Sergio
Lopez)
- Fix a warning when using large folio as the source of SPLICE_F_MOVE
on the fuse device (Bernd)
- Fix uninitialized value found by KMSAN (Luis Henriques)
- Fix synchronous INIT hang (Miklos)
- Fix race between inode initialization and FUSE_NOTIFY_INVAL_INODE
(Horst)
- Allow fd to be closed after passing fuse device fd to
fsconfig(..., "fd", ...) (Miklos)
- Support FSCONFIG_SET_FD for "fd" option (Miklos)
- Misc fixes and cleanups
* tag 'fuse-update-7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse: (21 commits)
fuse: support FSCONFIG_SET_FD for "fd" option
fuse: clean up device cloning
fuse: don't require /dev/fuse fd to be kept open during mount
fuse: add refcount to fuse_dev
fuse: create fuse_dev on /dev/fuse open instead of mount
fuse: check connection state on notification
fuse: fuse_dev_ioctl_clone() should wait for device file to be initialized
fuse: fix inode initialization race
fuse: abort on fatal signal during sync init
fuse: fix uninit-value in fuse_dentry_revalidate()
fuse: use offset_in_page() for page offset calculations
fuse: use DIV_ROUND_UP() for page count calculations
fuse: simplify logic in fuse_notify_store() and fuse_retrieve()
fuse: validate outarg offset and size in notify store/retrieve
fuse: Check for large folio with SPLICE_F_MOVE
fuse: quiet down complaints in fuse_conn_limit_write
fuse: drop unnecessary argument from fuse_lookup_init()
fuse: fix premature writetrhough request for large folio
fuse: refactor duplicate queue teardown operation
virtiofs: add FUSE protocol validation
...
When flushing out outstanding glock work during an unmount, gfs2_log_flush()
can be called when sdp->sd_jdesc has already been deallocated and sdp->sd_jdesc
is NULL. Commit 35264909e9d1 ("gfs2: Fix NULL pointer dereference in
gfs2_log_flush") added a check for that to gfs2_log_flush() itself, but it
missed the sdp->sd_jdesc dereference in gfs2_log_release(). Fix that.
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Closes: https://lore.kernel.org/r/202604071139.HNJiCaAi-lkp@intel.com/
Fixes: 35264909e9d1 ("gfs2: Fix NULL pointer dereference in gfs2_log_flush")
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Pull RTLA updates from Steven Rostedt:
- Simplify option parsing
Auto-generate getopt_long() optstring for short options from long
options array, avoiding the need to specify it manually and reducing
the surface for mistakes.
- Add unit tests
Implement unit tests (make unit-tests) using libcheck, next to
existing runtime tests (make check). Currently, three functions from
utils.c are tested.
- Add --stack-format option
In addition to stopping stack pointer decoding (with -s/--stack
option) on first unresolvable pointer, allow also skipping
unresolvable pointers and displaying everything, configurable with a
new option.
- Unify number of CPUs into one global variable
Use one global variable, nr_cpus, to store the number of CPUs instead
of retrieving it and passing it at multiple places.
- Fix behavior in various corner cases
Make RTLA behave correctly in several corner cases: memory allocation
failure, invalid value read from kernel side, thread creation
failure, malformed time value input, and read/write failure or
interruption by signal.
- Improve string handling
Simplify several places in the code that handle strings, including
parsing of action arguments. A few new helper functions and variables
are added for that purpose.
- Get rid of magic numbers
Few places handling paths use a magic number of 1024. Replace it with
MAX_PATH and ARRAY_SIZE() macro.
- Unify threshold handling
Code that handles response to latency threshold is duplicated between
tools, which has led to bugs in the past. Unify it into a new helper
as much as possible.
- Fix segfault on SIGINT during cleanup
The SIGINT handler touches dynamically allocated memory. Detach it
before freeing it during cleanup to prevent segmentation fault and
discarding of output buffers. Also, properly document SIGINT handling
while at it.
* tag 'trace-rtla-v7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (28 commits)
Documentation/rtla: Document SIGINT behavior
rtla: Fix segfault on multiple SIGINTs
rtla/utils: Fix loop condition in PID validation
rtla/utils: Fix resource leak in set_comm_sched_attr()
rtla/trace: Fix I/O handling in save_trace_to_file()
rtla/trace: Fix write loop in trace_event_save_hist()
rtla/timerlat: Simplify RTLA_NO_BPF environment variable check
rtla: Use str_has_prefix() for option prefix check
rtla: Enforce exact match for time unit suffixes
rtla: Use str_has_prefix() for prefix checks
rtla: Add str_has_prefix() helper function
rtla: Handle pthread_create() failure properly
rtla/timerlat: Add bounds check for softirq vector
rtla: Simplify code by caching string lengths
rtla: Replace magic number with MAX_PATH
rtla: Introduce common_threshold_handler() helper
rtla/actions: Simplify argument parsing
rtla: Use strdup() to simplify code
rtla: Exit on memory allocation failures during initialization
tools/rtla: Remove unneeded nr_cpus from for_each_monitored_cpu
...
This is not only cleaner to use in userspace (no need to sprintf the fd to
a string) but also allows userspace to detect that the devfd can be closed
after the fsconfig call.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
In gfs2_evict_inode(), don't issue error messages once a withdraw has already
occurred.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Pull runtime verification updates from Steven Rostedt:
- Refactor da_monitor header to share handlers across monitor types
No functional changes, only less code duplication.
- Add Hybrid Automata model class
Add a new model class that extends deterministic automata by adding
constraints on transitions and states. Those constraints can take
into account wall-clock time and as such allow RV monitor to make
assertions on real time. Add documentation and code generation
scripts.
- Add stall monitor as hybrid automaton example
Add a monitor that triggers a violation when a task is stalling as an
example of automaton working with real time variables.
- Convert the opid monitor to a hybrid automaton
The opid monitor can be heavily simplified if written as a hybrid
automaton: instead of tracking preempt and interrupt enable/disable
events, it can just run constraints on the preemption/interrupt
states when events like wakeup and need_resched verify.
- Add support for per-object monitors in DA/HA
Allow writing deterministic and hybrid automata monitors for generic
objects (e.g. any struct), by exploiting a hash table where objects
are saved. This allows to track more than just tasks in RV. For
instance it will be used to track deadline entities in deadline
monitors.
- Add deadline tracepoints and move some deadline utilities
Prepare the ground for deadline monitors by defining events and
exporting helpers.
- Add nomiss deadline monitor
Add first example of deadline monitor asserting all entities complete
before their deadline.
- Improve rvgen error handling
Introduce AutomataError exception class and better handle expected
exceptions while showing a backtrace for unexpected ones.
- Improve python code quality in rvgen
Refactor the rvgen generation scripts to align with python best
practices: use f-strings instead of %, use len() instead of
__len__(), remove semicolons, use context managers for file
operations, fix whitespace violations, extract magic strings into
constants, remove unused imports and methods.
- Fix small bugs in rvgen
The generator scripts presented some corner case bugs: logical error
in validating what a correct dot file looks like, fix an isinstance()
check, enforce a dot file has an initial state, fix type annotations
and typos in comments.
- rvgen refactoring
Refactor automata.py to use iterator-based parsing and handle
required arguments directly in argparse.
- Allow epoll in rtapp-sleep monitor
The epoll_wait call is now rt-friendly so it should be allowed in the
sleep monitor as a valid sleep method.
* tag 'trace-rv-v7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (32 commits)
rv: Allow epoll in rtapp-sleep monitor
rv/rvgen: fix _fill_states() return type annotation
rv/rvgen: fix unbound loop variable warning
rv/rvgen: enforce presence of initial state
rv/rvgen: extract node marker string to class constant
rv/rvgen: fix isinstance check in Variable.expand()
rv/rvgen: make monitor arguments required in rvgen
rv/rvgen: remove unused __get_main_name method
rv/rvgen: remove unused sys import from dot2c
rv/rvgen: refactor automata.py to use iterator-based parsing
rv/rvgen: use class constant for init marker
rv/rvgen: fix DOT file validation logic error
rv/rvgen: fix PEP 8 whitespace violations
rv/rvgen: fix typos in automata and generator docstring and comments
rv/rvgen: use context managers for file operations
rv/rvgen: remove unnecessary semicolons
rv/rvgen: replace __len__() calls with len()
rv/rvgen: replace % string formatting with f-strings
rv/rvgen: remove bare except clauses in generator
rv/rvgen: introduce AutomataError exception class
...
The behavior of RTLA on receiving SIGINT is currently undocumented.
Describe it in RTLA's common appendix that appears in man pages for all
RTLA tools to avoid confusion.
Suggested-by: Attila Fazekas <afazekas@redhat.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20260324123229.152424-1-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
- fuse_mutex is not needed for device cloning, because fuse_dev_install()
uses cmpxcg() to set fud->fc, which prevents races between clone/mount
or clone/clone. This makes the logic simpler
- Drop fc->dev_count. This is only used to check in release if the device
is the last clone, but checking list_empty(&fc->devices) is equivalent
after removing the released device from the list. Removing the fuse_dev
before calling fuse_abort_conn() is okay, since the processing and io
lists are now empty for this device.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
During an unmount, wait for potential withdraw to complete before calling
gfs2_make_fs_ro(). This will allow gfs2_make_fs_ro() to skip much of its work.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Pull ktest updates from Steven Rostedt:
- Fix undef warning when WARNINGS_FILE is unset
The check_buildlog() references WARNINGS_FILE even when it's not set.
Perl triggers a warning in this case. Check if the WARNINGS_FILE is
defined before checking if the file it represents exists.
- Fix how LOG_FILE is resolved
LOG_FILE is expanded immediately after the config file is parsed. If
LOG_FILE depends on variables from the tests it will use stale values
instead of using the test variables. Have LOG_FILE also resolve test
variables.
- Treat a undefined self reference variable as empty
Variables can recursively include itself for appending. Currently, if
the references itself and it is not defined, it leaves the variable
in the define: "VAR = ${VAR} foo" keeps the ${VAR} around. Have it
removed instead.
- Fix clearing of variables per tests
If a variable has a defined default, a test can not clear it by
assigning the variable to empty. Fix this by clearing the variable
for a test when the test config has that variable assigned to
nothing.
- Fix run_command() to catch stderr in the shell command parsing
Switch to Perl list form open to use "sh -c" wrapper to run shell
commands to have the log file catch shell parsing errors.
- Fix console output during reboot cycle
The POWER_CYCLE callback during reboot() can miss output from the
next boot making ktest miss the boot string it was waiting for.
- Add PRE_KTEST_DIE for PRE_KTEST failures
If the command for PRE_KTEST fails, ktest does not fail (this was by
design as this command was used to add patches that may or may not
apply). Add PRE_KTEST_DIE value to force ktest to fail if PRE_KTEST
fails.
- Run POST_KTEST hooks on failure and cancellation
PRE_KTEST always runs before a ktest test, have POST_KTEST always run
after a test even if the test fails or is cancelled to do the
teardown of PRE_KTEST.
- Add a --dry-run mode
Add --dry-run to parse the config, print the results and exit without
running any of the tests.
- Store failures from the dodie() path as well
The STORE_FAILURES saves the logs on failure, but there's failure
paths that miss storing. Perform STORE_FAILURES in dodie() to capture
these failures too.
* tag 'ktest-v7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-ktest:
ktest: Store failure logs also in fatal paths
ktest: Add a --dry-run mode
ktest: Run POST_KTEST hooks on failure and cancellation
ktest: Add PRE_KTEST_DIE for PRE_KTEST failures
ktest: Stop dropping console output during power-cycle reboot
ktest: Run commands through list-form shell open
ktest: Honor empty per-test option overrides
ktest: Treat undefined self-reference as empty
ktest: Resolve LOG_FILE in test option context
ktest: Avoid undef warning when WARNINGS_FILE is unset
Since commit 0c43094f8cc9 ("eventpoll: Replace rwlock with spinlock"),
epoll_wait is real-time-safe syscall for sleeping.
Add epoll_wait to the list of rt-safe sleeping APIs.
Signed-off-by: Nam Cao <namcao@linutronix.de>
Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
Link: https://lore.kernel.org/r/20260401130828.3115428-1-namcao@linutronix.de
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Detach stop_trace() from SIGINT/SIGALRM on tool clean-up to prevent it
from crashing RTLA by accessing freed memory.
This prevents a crash when multiple SIGINTs are received.
Fixes: d6899e560366 ("rtla/timerlat_hist: Abort event processing on second signal")
Fixes: 80967b354a76 ("rtla/timerlat_top: Abort event processing on second signal")
Reviewed-by: Wander Lairson Costa <wander@redhat.com>
Link: https://lore.kernel.org/r/20260310160725.144443-1-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
With the new mount API the sequence of syscalls would be:
fs_fd = fsopen("fuse", 0);
snprintf(opt, sizeof(opt), "%i", devfd);
fsconfig(fs_fd, FSCONFIG_SET_STRING, "fd", opt, 0);
/* ... */
fsconfig(fs_fd, FSCONFIG_CMD_CREATE, 0, 0, 0);
Current mount code just stores the value of devfd in the fs_context and
uses it in during FSCONFIG_CMD_CREATE, which is inelegant.
Instead grab a reference to the underlying fuse_dev, and use that during
the filesystem creation.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
In gfs2_dinode_in(), only allow directories to have the GFS2_DIF_EXHASH
flag set. This will prevent other parts of the code from treating
regular inodes as directories based on the presence of that flag.
In sweep_bh_for_rgrps() and __gfs2_free_blocks(), check if the
GFS2_DIF_EXHASH flag is set instead of checking if i_depth is non-zero.
This matches what the directory code does. (The i_depth checks were
introduced in commit 6d3117b412951 ("GFS2: Wipe directory hash table
metadata when deallocating a directory").)
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Pull tracefs updates from Steven Rostedt:
- Simplify error handling with guards()
Use guards() to simplify the handling of releasing locks in exit
paths.
- Use dentry name snapshots instead of allocation
Instead of allocating a temp buffer to store the dentry name to use
in mkdir() and rmdir() use take_dentry_name_snapshot().
- Fix default permissions not being applied at boot
The default permissions for tracefs was 0700 to only allow root
having access. But after a change to fix other mount options the
update to permissions ignored the defined default and used the system
default of 0755. This is a regression and is fixed.
* tag 'tracefs-v7.1-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracefs: Removed unused 'ret' variable in eventfs_iterate()
tracefs: Fix default permissions not being applied on initial mount
tracefs: Use dentry name snapshots instead of heap allocation
eventfs: Simplify code using guard()s
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