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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This converts some of the visually simpler cases that have been split
over multiple lines. I only did the ones that are easy to verify the
resulting diff by having just that final GFP_KERNEL argument on the next
line.
Somebody should probably do a proper coccinelle script for this, but for
me the trivial script actually resulted in an assertion failure in the
middle of the script. I probably had made it a bit _too_ trivial.
So after fighting that far a while I decided to just do some of the
syntactically simpler cases with variations of the previous 'sed'
scripts.
The more syntactically complex multi-line cases would mostly really want
whitespace cleanup anyway.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This is the exact same thing as the 'alloc_obj()' version, only much
smaller because there are a lot fewer users of the *alloc_flex()
interface.
As with alloc_obj() version, this was done entirely with mindless brute
force, using the same script, except using 'flex' in the pattern rather
than 'objs*'.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This was done entirely with mindless brute force, using
git grep -l '\<k[vmz]*alloc_objs*(.*, GFP_KERNEL)' |
xargs sed -i 's/\(alloc_objs*(.*\), GFP_KERNEL)/\1)/'
to convert the new alloc_obj() users that had a simple GFP_KERNEL
argument to just drop that argument.
Note that due to the extreme simplicity of the scripting, any slightly
more complex cases spread over multiple lines would not be triggered:
they definitely exist, but this covers the vast bulk of the cases, and
the resulting diff is also then easier to check automatically.
For the same reason the 'flex' versions will be done as a separate
conversion.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Most simple allocations use GFP_KERNEL, and with the new allocation
helpers being introduced, let's just take advantage of that to simplify
that default case.
It's a numbers game:
git grep 'alloc_obj(' |
sed 's/.*\(GFP_[_A-Z]*\).*/\1/' |
sort | uniq -c | sort -n | tail
shows that about 90% of all those new allocator instances just use that
standard GFP_KERNEL.
Those helpers are already macros, and we can easily just make it be the
default case when the gfp argument is missing.
And yes, we could do that for all the legacy interfaces too, but let's
keep it to just the new ones at least for now, since those all got
converted recently anyway, so this is not any "extra" noise outside of
that limited conversion.
And, in fact, I want to do this before doing the -rc1 release, exactly
so that we don't get extra merge conflicts.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Commit 69050f8d6d07 ("treewide: Replace kmalloc with kmalloc_obj for
non-scalar types") started using the new allocation helpers, and in the
process showed that they were completely non-working.
The overflow logic in overflows_flex_counter_type() is completely the
wrong way around, and that broke __alloc_flex() completely. By chance,
the resulting code was then such a mess that clang generated
sufficiently garbage code that objtool warned about it all. Which made
it somewhat quicker to narrow things down.
While fixing overflows_flex_counter_type() would presumably fix this
all, I'm excising the whole broken overflow logic from __alloc_flex(),
because we don't want that kind of code in basic allocation functions
anyway.
That (no longer) broken overflows_flex_counter_type() thing needs to be
inserted into the actual __set_flex_counter() logic in the unlikely case
that we ever want this at all. And made conditional.
Fixes: 81cee9166a90 ("compiler_types: Introduce __flex_counter() and family")
Fixes: 69050f8d6d07 ("treewide: Replace kmalloc with kmalloc_obj for non-scalar types")
Cc: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/all/CAHk-=whEd020BYzGTzYrENjD9Z5_82xx6h8HsQvH5xDSnv0=Hw@mail.gmail.com/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull kmalloc_obj conversion from Kees Cook:
"This does the tree-wide conversion to kmalloc_obj() and friends using
coccinelle, with a subsequent small manual cleanup of whitespace
alignment that coccinelle does not handle.
This uncovered a clang bug in __builtin_counted_by_ref(), so the
conversion is preceded by disabling that for current versions of
clang. The imminent clang 22.1 release has the fix.
I've done allmodconfig build tests for x86_64, arm64, i386, and arm. I
did defconfig builds for alpha, m68k, mips, parisc, powerpc, riscv,
s390, sparc, sh, arc, csky, xtensa, hexagon, and openrisc"
* tag 'kmalloc_obj-treewide-v7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
kmalloc_obj: Clean up after treewide replacements
treewide: Replace kmalloc with kmalloc_obj for non-scalar types
compiler_types: Disable __builtin_counted_by_ref for Clang
Pull perf tools updates from Arnaldo Carvalho de Melo:
- Introduce 'perf sched stats' tool with record/report/diff workflows
using schedstat counters
- Add a faster libdw based addr2line implementation and allow selecting
it or its alternatives via 'perf config addr2line.style='
- Data-type profiling fixes and improvements including the ability to
select fields using 'perf report''s -F/-fields, e.g.:
'perf report --fields overhead,type'
- Add 'perf test' regression tests for Data-type profiling with C and
Rust workloads
- Fix srcline printing with inlines in callchains, make sure this has
coverage in 'perf test'
- Fix printing of leaf IP in LBR callchains
- Fix display of metrics without sufficient permission in 'perf stat'
- Print all machines in 'perf kvm report -vvv', not just the host
- Switch from SHA-1 to BLAKE2s for build ID generation, remove SHA-1
code
- Fix 'perf report's histogram entry collapsing with '-F' option
- Use system's cacheline size instead of a hardcoded value in 'perf
report'
- Allow filtering conversion by time range in 'perf data'
- Cover conversion to CTF using 'perf data' in 'perf test'
- Address newer glibc const-correctness (-Werror=discarded-qualifiers)
issues
- Fixes and improvements for ARM's CoreSight support, simplify ARM SPE
event config in 'perf mem', update docs for 'perf c2c' including the
ARM events it can be used with
- Build support for generating metrics from arch specific python
script, add extra AMD, Intel, ARM64 metrics using it
- Add AMD Zen 6 events and metrics
- Add JSON file with OpenHW Risc-V CVA6 hardware counters
- Add 'perf kvm' stats live testing
- Add more 'perf stat' tests to 'perf test'
- Fix segfault in `perf lock contention -b/--use-bpf`
- Fix various 'perf test' cases for s390
- Build system cleanups, bump minimum shellcheck version to 0.7.2
- Support building the capstone based annotation routines as a plugin
- Allow passing extra Clang flags via EXTRA_BPF_FLAGS
* tag 'perf-tools-for-v7.0-1-2026-02-21' of git://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools: (255 commits)
perf test script: Add python script testing support
perf test script: Add perl script testing support
perf script: Allow the generated script to be a path
perf test: perf data --to-ctf testing
perf test: Test pipe mode with data conversion --to-json
perf json: Pipe mode --to-ctf support
perf json: Pipe mode --to-json support
perf check: Add libbabeltrace to the listed features
perf build: Allow passing extra Clang flags via EXTRA_BPF_FLAGS
perf test data_type_profiling.sh: Skip just the Rust tests if code_with_type workload is missing
tools build: Fix feature test for rust compiler
perf libunwind: Fix calls to thread__e_machine()
perf stat: Add no-affinity flag
perf evlist: Reduce affinity use and move into iterator, fix no affinity
perf evlist: Missing TPEBS close in evlist__close()
perf evlist: Special map propagation for tool events that read on 1 CPU
perf stat-shadow: In prepare_metric fix guard on reading NULL perf_stat_evsel
Revert "perf tool_pmu: More accurately set the cpus for tool events"
tools build: Emit dependencies file for test-rust.bin
tools build: Make test-rust.bin be removed by the 'clean' target
...
Coccinelle doesn't handle re-indenting line escapes. Fix the 2 places
where these got misaligned.
Remove 2 now-redundant type casts, found with:
$ git grep -P 'struct (\S+).*\)\s*k\S+alloc_(objs?|flex)\(struct \1'
Signed-off-by: Kees Cook <kees@kernel.org>
Pull coccinelle updates from Julia Lawall:
"This simplifies and clarifies the handling of output generated by
Coccinelle that is sent to standard error.
By default, this goes to /dev/null. Remind the user of that and
encourage them to provide another file name (Benjamin Philip)"
* tag 'cocci-7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jlawall/linux:
Documentation: Coccinelle: document debug log handling
scripts: coccicheck: warn on unset debug file
scripts: coccicheck: simplify debug file handling
Basic coverage of python script support from `perf script`.
Committer testing:
$ perf test 'perf script python'
107: perf script python tests : Ok
$ perf test -vv 'perf script python'
107: perf script python tests:
--- start ---
test child forked, pid 595537
Testing event: sched:sched_switch
perf script python test [Skipped: failed to record sched:sched_switch]
Testing event: task-clock
Generating python script...
generated Python script: /tmp/__perf_test_script.J4rWj.py
Executing python script...
perf script python test [Success: task-clock triggered param_dict]
---- end(0) ----
107: perf script python tests : Ok
$
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Yujie Liu <yujie.liu@intel.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:
Single allocations: kmalloc(sizeof(TYPE), ...)
are replaced with: kmalloc_obj(TYPE, ...)
Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with: kmalloc_objs(TYPE, COUNT, ...)
Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...)
(where TYPE may also be *VAR)
The resulting allocations no longer return "void *", instead returning
"TYPE *".
Signed-off-by: Kees Cook <kees@kernel.org>
Pull NTB (PCIe non-transparent bridge) updates from Jon Mason:
"NTB updates include debugfs improvements, correctness fixes, cleanups,
and new hardware support:
ntb_transport QP stats are converted to seq_file, a tx_memcpy_offload
module parameter is introduced with associated ordering fixes, and a
debugfs queue name truncation bug is corrected.
Additional fixes address format specifier mismatches in ntb_tool and
boundary conditions in the Switchtec driver, while unused MSI helpers
are removed and the codebase migrates to dma_map_phys().
Intel Gen6 (Diamond Rapids) NTB support is also added"
* tag 'ntb-7.0' of https://github.com/jonmason/ntb:
NTB: ntb_transport: Use seq_file for QP stats debugfs
NTB: ntb_transport: Fix too small buffer for debugfs_name
ntb/ntb_tool: correct sscanf format for u64 and size_t in tool_peer_mw_trans_write
ntb: intel: Add Intel Gen6 NTB support for DiamondRapids
NTB/msi: Remove unused functions
ntb: ntb_hw_switchtec: Increase MAX_MWS limit to 256
ntb: ntb_hw_switchtec: Fix array-index-out-of-bounds access
ntb: ntb_hw_switchtec: Fix shift-out-of-bounds for 0 mw lut
NTB: epf: allow built-in build
ntb: migrate to dma_map_phys instead of map_page
NTB: ntb_transport: Add 'tx_memcpy_offload' module option
NTB: ntb_transport: Remove unused 'retries' field from ntb_queue_entry
The current debug documentation does not mention that logs are printed
to stdout unless DEBUG_FILE is set. It also doesn't mention that
Coccinelle cannot overwrite debug files.
Document this behaviour in the examples and reference it in the
debugging section.
Signed-off-by: Benjamin Philip <benjamin.philip495@gmail.com>
Signed-off-by: Julia Lawall <julia.lawall@inria.fr>
Basic coverage of perl script support from `perf script`. This is
disabled by default and so the test will most normally skip.
Committer testing:
$ perf test 'perf script perl'
106: perf script perl tests : Skip
$ perf test -vv 'perf script perl'
106: perf script perl tests:
--- start ---
test child forked, pid 578323
perf script perl test [Skipped: no libperl support]
---- end(-2) ----
106: perf script perl tests : Skip
$ perf check feature libperl
libperl: [ OFF ] # HAVE_LIBPERL_SUPPORT ( tip: Deprecated, use LIBPERL=1 and install perl-ExtUtils-Embed/libperl-dev to build with it )
$
Install perl-ExtUtils-Embed, build with LIBPERL=1, rebuild:
$ perf check feature libperl
libperl: [ on ] # HAVE_LIBPERL_SUPPORT
$ perf test 'perf script perl'
106: perf script perl tests : Ok
$ perf test -vv 'perf script perl'
106: perf script perl tests:
--- start ---
test child forked, pid 588206
Testing event: sched:sched_switch
perf script perl test [Skipped: failed to record sched:sched_switch]
Testing event: task-clock
Generating perl script...
generated Perl script: /tmp/__perf_test_script.RpMn5.pl
Executing perl script...
perf script perl test [Success: task-clock triggered $VAR1]
---- end(0) ----
106: perf script perl tests : Ok
$
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Yujie Liu <yujie.liu@intel.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Unfortunately, there is a corner case of __builtin_counted_by_ref()
usage that crashes[1] Clang since support was introduced in Clang 19.
Disable it prior to Clang 22. Found while tested kmalloc_obj treewide
refactoring (via kmalloc_flex() usage).
Link: https://github.com/llvm/llvm-project/issues/182575 [1]
Signed-off-by: Kees Cook <kees@kernel.org>
Pull io_uring fixes from Jens Axboe:
- A fix for a missing URING_CMD128 opcode check, fixing an issue with
the SQE mixed mode support introduced in 6.19. Merged late due to
having multiple dependencies
- Add sqe->cmd size checking for big SQEs, similar to what we have for
normal sized SQEs
- Fix a race condition in zcrx, that leads to a double free
* tag 'io_uring-20260221' of git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux:
io_uring: Add size check for sqe->cmd
io_uring: add IORING_OP_URING_CMD128 to opcode checks
io_uring/zcrx: fix user_ref race between scrub and refill paths
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