tjh.dev
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 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 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 RISC-V fixes from Paul Walmsley:
"Notable changes include a fix to close one common microarchitectural
attack vector for out-of-order cores. Another patch exposed an
omission in my boot test coverage, which is currently missing
relocatable kernels. Otherwise, the fixes seem to be settling down for
us.
- Fix CONFIG_RELOCATABLE=y boots by building Image files from
vmlinux, rather than vmlinux.unstripped, now that the .modinfo
section is included in vmlinux.unstripped
- Prevent branch predictor poisoning microarchitectural attacks that
use the syscall index as a vector by using array_index_nospec() to
clamp the index after the bounds check (as x86 and ARM64 already
do)
- Fix a crash in test_kprobes when building with Clang
- Fix a deadlock possible when tracing is enabled for SBI ecalls
- Fix the definition of the Zk standard RISC-V ISA extension bundle,
which was missing the Zknh extension
- A few other miscellaneous non-functional cleanups, removing unused
macros, fixing an out-of-date path in code comments, resolving a
compile-time warning for a type mismatch in a pr_crit(), and
removing an unnecessary header file inclusion"
* tag 'riscv-for-linus-6.19-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux:
riscv: trace: fix snapshot deadlock with sbi ecall
riscv: remove irqflags.h inclusion in asm/bitops.h
riscv: cpu_ops_sbi: smp_processor_id() returns int, not unsigned int
riscv: configs: Clean up references to non-existing configs
riscv: kexec_image: Fix dead link to boot-image-header.rst
riscv: pgtable: Cleanup useless VA_USER_XXX definitions
riscv: cpufeature: Fix Zk bundled extension missing Zknh
riscv: fix KUnit test_kprobes crash when building with Clang
riscv: Sanitize syscall table indexing under speculation
riscv: boot: Always make Image from vmlinux, not vmlinux.unstripped
Pull driver core fixes from Danilo Krummrich:
- Fix swapped example values for the `family` and `machine` attributes
in the sysfs SoC bus ABI documentation
- Fix Rust build and intra-doc issues when optional subsystems
(CONFIG_PCI, CONFIG_AUXILIARY_BUS, CONFIG_PRINTK) are disabled
- Fix typos and incorrect safety comments in Rust PCI, DMA, and
device ID documentation
* tag 'driver-core-6.19-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core:
rust: device: Remove explicit import of CStrExt
rust: pci: fix typos in Bar struct's comments
rust: device: fix broken intra-doc links
rust: dma: fix broken intra-doc links
rust: driver: fix broken intra-doc links to example driver types
rust: device_id: replace incorrect word in safety documentation
rust: dma: remove incorrect safety documentation
docs: ABI: sysfs-devices-soc: Fix swapped sample values
If sbi_ecall.c's functions are traceable,
echo "__sbi_ecall:snapshot" > /sys/kernel/tracing/set_ftrace_filter
may get the kernel into a deadlock.
(Functions in sbi_ecall.c are excluded from tracing if
CONFIG_RISCV_ALTERNATIVE_EARLY is set.)
__sbi_ecall triggers a snapshot of the ringbuffer. The snapshot code
raises an IPI interrupt, which results in another call to __sbi_ecall
and another snapshot...
All it takes to get into this endless loop is one initial __sbi_ecall.
On RISC-V systems without SSTC extension, the clock events in
timer-riscv.c issue periodic sbi ecalls, making the problem easy to
trigger.
Always exclude the sbi_ecall.c functions from tracing to fix the
potential deadlock.
sbi ecalls can easiliy be logged via trace events, excluding ecall
functions from function tracing is not a big limitation.
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://patch.msgid.link/20251223135043.1336524-1-martin@kaiser.cx
Signed-off-by: Paul Walmsley <pjw@kernel.org>
Pull kselftest fix from Shuah Khan:
"Fix tracing test_multiple_writes stalls when buffer_size_kb is less
than 12KB"
* tag 'linux_kselftest-fixes-6.19-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest:
selftests/tracing: Fix test_multiple_writes stall
Remove the explicit import of CStrExt. When CONFIG_PRINTK is disabled
this import causes a build error:
error: unused import: `crate::str::CStrExt`
--> rust/kernel/device.rs:17:5
|
17 | use crate::str::CStrExt as _;
| ^^^^^^^^^^^^^^^^^^^
|
= note: `-D unused-imports` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(unused_imports)]`
error: aborting due to 1 previous error
CStrExt is covered by prelude::* so the explicit import is redundant.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Fixes: 3b83f5d5e78a ("rust: replace `CStr` with `core::ffi::CStr`")
Link: https://patch.msgid.link/20260106000320.2593800-1-fujita.tomonori@gmail.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
The arch/riscv/include/asm/bitops.h does not functionally require
including /linux/irqflags.h. Additionally, adding
arch/riscv/include/asm/percpu.h causes a circular inclusion:
kernel/bounds.c
->include/linux/log2.h
->include/linux/bitops.h
->arch/riscv/include/asm/bitops.h
->include/linux/irqflags.h
->include/linux/find.h
->return val ? __ffs(val) : size;
->arch/riscv/include/asm/bitops.h
The compilation log is as follows:
CC kernel/bounds.s
In file included from ./include/linux/bitmap.h:11,
from ./include/linux/cpumask.h:12,
from ./arch/riscv/include/asm/processor.h:55,
from ./arch/riscv/include/asm/thread_info.h:42,
from ./include/linux/thread_info.h:60,
from ./include/asm-generic/preempt.h:5,
from ./arch/riscv/include/generated/asm/preempt.h:1,
from ./include/linux/preempt.h:79,
from ./arch/riscv/include/asm/percpu.h:8,
from ./include/linux/irqflags.h:19,
from ./arch/riscv/include/asm/bitops.h:14,
from ./include/linux/bitops.h:68,
from ./include/linux/log2.h:12,
from kernel/bounds.c:13:
./include/linux/find.h: In function 'find_next_bit':
./include/linux/find.h:66:30: error: implicit declaration of function '__ffs' [-Wimplicit-function-declaration]
66 | return val ? __ffs(val) : size;
| ^~~~~
Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
Acked-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Link: https://patch.msgid.link/20251216014721.42262-2-cuiyunhui@bytedance.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>
Pull iomu fixes from Joerg Roedel:
- several Kconfig-related build fixes
- fix for when gcc 8.5 on PPC refuses to inline a function from a
header file
* tag 'iommu-fixes-v6.19-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/iommu/linux:
iommupt: Make pt_feature() always_inline
iommufd/selftest: Prevent module/builtin conflicts in kconfig
iommufd/selftest: Add missing kconfig for DMA_SHARED_BUFFER
iommupt: Fix the kunit building
When /sys/kernel/tracing/buffer_size_kb is less than 12KB,
the test_multiple_writes test will stall and wait for more
input due to insufficient buffer space.
Check current buffer_size_kb value before the test. If it is
less than 12KB, it temporarily increase the buffer to 12KB,
and restore the original value after the tests are completed.
Link: https://lore.kernel.org/r/20260109033620.25727-1-fushuai.wang@linux.dev
Fixes: 37f46601383a ("selftests/tracing: Add basic test for trace_marker_raw file")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Fushuai Wang <wangfushuai@baidu.com>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Fix a typo in the doc-comment of the Bar structure: 'inststance ->
instance'.
Add also 'is' to the comment inside Bar's `new()` function (suggested
by Dirk):
// `pdev` is valid by the invariants of `Device`.
Fixes: bf9651f84b4e ("rust: pci: implement I/O mappable `pci::Bar`")
Suggested-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Marko Turk <mt@markoturk.info>
Reviewed-by: Dirk Behme <dirk.behme@de.bosch.com>
Link: https://patch.msgid.link/20260105213726.73000-2-mt@markoturk.info
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
The print in sbi_cpu_stop() assumes smp_processor_id() returns an
unsigned int, when it is actually an int. Fix the format string to
avoid mismatch type warnings in rht pr_crit().
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Link: https://patch.msgid.link/20260102145839.657864-1-ben.dooks@codethink.co.uk
Signed-off-by: Paul Walmsley <pjw@kernel.org>
Sheng Yong reported [1] that Android APEX images didn't work with commit
072a7c7cdbea ("erofs: don't bother with s_stack_depth increasing for
now") because "EROFS-formatted APEX file images can be stored within an
EROFS-formatted Android system partition."
In response, I sent a quick fat-fingered [PATCH v3] to address the
report. Unfortunately, the updated condition was incorrect:
if (erofs_is_fileio_mode(sbi)) {
- sb->s_stack_depth =
- file_inode(sbi->dif0.file)->i_sb->s_stack_depth + 1;
- if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
- erofs_err(sb, "maximum fs stacking depth exceeded");
+ inode = file_inode(sbi->dif0.file);
+ if ((inode->i_sb->s_op == &erofs_sops && !sb->s_bdev) ||
+ inode->i_sb->s_stack_depth) {
The condition `!sb->s_bdev` is always true for all file-backed EROFS
mounts, making the check effectively a no-op.
The real fix tested and confirmed by Sheng Yong [2] at that time was
[PATCH v3 RESEND], which correctly ensures the following EROFS^2 setup
works:
EROFS (on a block device) + EROFS (file-backed mount)
But sadly I screwed it up again by upstreaming the outdated [PATCH v3].
This patch applies the same logic as the delta between the upstream
[PATCH v3] and the real fix [PATCH v3 RESEND].
Reported-by: Sheng Yong <shengyong1@xiaomi.com>
Closes: https://lore.kernel.org/r/3acec686-4020-4609-aee4-5dae7b9b0093@gmail.com [1]
Fixes: 072a7c7cdbea ("erofs: don't bother with s_stack_depth increasing for now")
Link: https://lore.kernel.org/r/243f57b8-246f-47e7-9fb1-27a771e8e9e8@gmail.com [2]
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
gcc 8.5 on powerpc does not automatically inline these functions even
though they evaluate to constants in key cases. Since the constant
propagation is essential for some code elimination and built-time checks
this causes a build failure:
ERROR: modpost: "__pt_no_sw_bit" [drivers/iommu/generic_pt/fmt/iommu_amdv1.ko] undefined!
Caused by this:
if (pts_feature(&pts, PT_FEAT_DMA_INCOHERENT) &&
!pt_test_sw_bit_acquire(&pts,
SW_BIT_CACHE_FLUSH_DONE))
flush_writes_item(&pts);
Where pts_feature() evaluates to a constant false. Mark them as
__always_inline to force it to evaluate to a constant and trigger the code
elimination.
Fixes: 7c5b184db714 ("genpt: Generic Page Table base API")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512230720.9y9DtWIo-lkp@intel.com/
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
The `pci` module is conditional on CONFIG_PCI. When it's disabled, the
intra-doc link to `pci::Device` causes rustdoc warnings:
warning: unresolved link to `kernel::pci::Device`
--> rust/kernel/device.rs:163:22
|
163 | /// [`pci::Device`]: kernel::pci::Device
| ^^^^^^^^^^^^^^^^^^^ no item named `pci` in module `kernel`
|
= note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default
Fix this by making the documentation conditional on CONFIG_PCI.
Fixes: d6e26c1ae4a6 ("device: rust: expand documentation for Device")
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Dirk Behme <dirk.behme@de.bosch.com>
Link: https://patch.msgid.link/20251231045728.1912024-2-fujita.tomonori@gmail.com
[ Keep the "such as" part indicating a list of examples; fix typos in
commit message. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
- Drop 'CONFIG_I2C_COMPAT is not set' (removed in commit 7e722083fcc3
("i2c: Remove I2C_COMPAT config symbol and related code"))
- Drop 'CONFIG_SCHED_DEBUG is not set' (removed in commit b52173065e0a
("sched/debug: Remove CONFIG_SCHED_DEBUG"))
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Link: https://patch.msgid.link/20260107092425.24737-1-lukas.bulwahn@redhat.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>
Pull erofs fix from Gao Xiang:
- Don't increase s_stack_depth which caused regressions in some
composefs mount setups (EROFS + ovl^2)
Instead just allow one extra unaccounted fs stacking level for
straightforward cases.
* tag 'erofs-for-6.19-rc5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs:
erofs: don't bother with s_stack_depth increasing for now
The selftest now depends on the AMDv1 page table, however the selftest
kconfig itself is just an sub-option of the main IOMMUFD module kconfig.
This means it cannot be modular and so kconfig allowed a modular
IOMMU_PT_AMDV1 with a built in IOMMUFD. This causes link failures:
ld: vmlinux.o: in function `mock_domain_alloc_pgtable.isra.0':
selftest.c:(.text+0x12e8ad3): undefined reference to `pt_iommu_amdv1_init'
ld: vmlinux.o: in function `BSWAP_SHUFB_CTL':
sha1-avx2-asm.o:(.rodata+0xaa36a8): undefined reference to `pt_iommu_amdv1_read_and_clear_dirty'
ld: sha1-avx2-asm.o:(.rodata+0xaa36f0): undefined reference to `pt_iommu_amdv1_map_pages'
ld: sha1-avx2-asm.o:(.rodata+0xaa36f8): undefined reference to `pt_iommu_amdv1_unmap_pages'
ld: sha1-avx2-asm.o:(.rodata+0xaa3720): undefined reference to `pt_iommu_amdv1_iova_to_phys'
Adjust the kconfig to disable IOMMUFD_TEST if IOMMU_PT_AMDV1 is incompatible.
Fixes: e93d5945ed5b ("iommufd: Change the selftest to use iommupt instead of xarray")
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512210135.freQWpxa-lkp@intel.com/
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
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