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 SCSI fixes from James Bottomley:
"Two core changes and the rest in drivers, one core change to quirk the
behaviour of the Iomega Zip drive and one to fix a hang caused by tag
reallocation problems, which has mostly been seen by the iscsi client.
Note the latter fixes the problem but still has a slight sysfs memory
leak, so will be amended in the next pull request (once we've run the
fix for the fix through our testing)"
* tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
scsi: target: Fix recursive locking in __configfs_open_file()
scsi: devinfo: Add BLIST_SKIP_IO_HINTS for Iomega ZIP
scsi: mpi3mr: Clear reset history on ready and recheck state after timeout
scsi: core: Fix refcount leak for tagset_refcnt
Pull fbdev fix from Helge Deller:
"Silence build error in au1100fb driver found by kernel test robot"
* tag 'fbdev-for-7.0-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/linux-fbdev:
fbdev: au1100fb: Fix build on MIPS64
In flush_write_buffer, &p->frag_sem is acquired and then the loaded store
function is called, which, here, is target_core_item_dbroot_store(). This
function called filp_open(), following which these functions were called
(in reverse order), according to the call trace:
down_read
__configfs_open_file
do_dentry_open
vfs_open
do_open
path_openat
do_filp_open
file_open_name
filp_open
target_core_item_dbroot_store
flush_write_buffer
configfs_write_iter
target_core_item_dbroot_store() tries to validate the new file path by
trying to open the file path provided to it; however, in this case, the bug
report shows:
db_root: not a directory: /sys/kernel/config/target/dbroot
indicating that the same configfs file was tried to be opened, on which it
is currently working on. Thus, it is trying to acquire frag_sem semaphore
of the same file of which it already holds the semaphore obtained in
flush_write_buffer(), leading to acquiring the semaphore in a nested manner
and a possibility of recursive locking.
Fix this by modifying target_core_item_dbroot_store() to use kern_path()
instead of filp_open() to avoid opening the file using filesystem-specific
function __configfs_open_file(), and further modifying it to make this fix
compatible.
Reported-by: syzbot+f6e8174215573a84b797@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f6e8174215573a84b797
Tested-by: syzbot+f6e8174215573a84b797@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Prithvi Tambewagh <activprithvi@gmail.com>
Reviewed-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Link: https://patch.msgid.link/20260216062002.61937-1-activprithvi@gmail.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Pull parisc fixes from Helge Deller:
"While testing Sasha Levin's 'kallsyms: embed source file:line info in
kernel stack traces' patch series, which increases the typical kernel
image size, I found some issues with the parisc initial kernel mapping
which may prevent the kernel to boot.
The three small patches here fix this"
* tag 'parisc-for-7.0-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux:
parisc: Fix initial page table creation for boot
parisc: Check kernel mapping earlier at bootup
parisc: Increase initial mapping to 64 MB with KALLSYMS
Fix an error reported by the kernel test robot:
au1100fb.c: error: implicit declaration of function 'KSEG1ADDR'; did you mean 'CKSEG1ADDR'?
arch/mips/include/asm/addrspace.h defines KSEG1ADDR only for 32 bit
configurations. So provide its compile-test stub also for 64bit mips builds.
Fixes: 6f366e86481a ("fbdev: au1100fb: Make driver compilable on non-mips platforms")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202603042127.PT6LuKqi-lkp@intel.com/
Signed-off-by: Helge Deller <deller@gmx.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
The Iomega ZIP 100 (Z100P2) can't process IO Advice Hints Grouping mode
page query. It immediately switches to the status phase 0xb8 after
receiving the subpage code 0x05 of MODE_SENSE_10 command, which fails
imm_out() and turns into DID_ERROR of this command, which leads to unusable
device. This was tested with an Iomega ZIP 100 (Z100P2) connected with a
StarTech PEX1P2 AX99100 PCIe parallel port card.
Prior to this fix, Test Unit Ready fails and the drive can't be used:
IMM: returned SCSI status b8
sd 7:0:6:0: [sdh] Test Unit Ready failed: Result: hostbyte=0x01 driverbyte=DRIVER_OK
Signed-off-by: Florian Fuchs <fuchsfl@gmail.com>
Link: https://patch.msgid.link/20260227181823.892932-1-fuchsfl@gmail.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Pull bpf fixes from Alexei Starovoitov:
- Fix u32/s32 bounds when ranges cross min/max boundary (Eduard
Zingerman)
- Fix precision backtracking with linked registers (Eduard Zingerman)
- Fix linker flags detection for resolve_btfids (Ihor Solodrai)
- Fix race in update_ftrace_direct_add/del (Jiri Olsa)
- Fix UAF in bpf_trampoline_link_cgroup_shim (Lang Xu)
* tag 'bpf-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf:
resolve_btfids: Fix linker flags detection
selftests/bpf: add reproducer for spurious precision propagation through calls
bpf: collect only live registers in linked regs
Revert "selftests/bpf: Update reg_bound range refinement logic"
selftests/bpf: test refining u32/s32 bounds when ranges cross min/max boundary
bpf: Fix u32/s32 bounds when ranges cross min/max boundary
bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim
ftrace: Add missing ftrace_lock to update_ftrace_direct_add/del
The KERNEL_INITIAL_ORDER value defines the initial size (usually 32 or
64 MB) of the page table during bootup. Up until now the whole area was
initialized with PTE entries, but there was no check if we filled too
many entries. Change the code to fill up with so many entries that the
"_end" symbol can be reached by the kernel, but not more entries than
actually fit into the initial PTE tables.
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: <stable@vger.kernel.org> # v6.0+
The driver retains reset history even after the IOC has successfully
reached the READY state. That leaves stale reset information active during
normal operation and can mislead recovery and diagnostics. In addition, if
the IOC becomes READY just as the ready timeout loop exits, the driver
still follows the failure path and may retry or report failure incorrectly.
Clear reset history once READY is confirmed so driver state matches actual
IOC status. After the timeout loop, recheck the IOC state and treat READY
as success instead of failing.
Signed-off-by: Ranjan Kumar <ranjan.kumar@broadcom.com>
Link: https://patch.msgid.link/20260225082622.82588-1-ranjan.kumar@broadcom.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Pull RCU selftest fixes from Boqun Feng:
"Fix a regression in RCU torture test pre-defined scenarios caused by
commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")
which limits PREEMPT_NONE to architectures that do not support
preemption at all and PREEMPT_VOLUNTARY to those architectures that do
not yet have PREEMPT_LAZY support.
Since major architectures (e.g. x86 and arm64) no longer support
CONFIG_PREEMPT_NONE and CONFIG_PREEMPT_VOLUNTARY, using them in
rcutorture, rcuscale, refscale, and scftorture pre-defined scenarios
causes config checking errors.
Switch these kconfigs to PREEMPT_LAZY"
* tag 'rcu-fixes.v7.0-20260307a' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux:
scftorture: Update due to x86 not supporting none/voluntary preemption
refscale: Update due to x86 not supporting none/voluntary preemption
rcuscale: Update due to x86 not supporting none/voluntary preemption
rcutorture: Update due to x86 not supporting none/voluntary preemption
The "|| echo -lzstd" default makes zstd an unconditional link
dependency of resolve_btfids. On systems where libzstd-dev is not
installed and pkg-config fails, the linker fails:
ld: cannot find -lzstd: No such file or directory
libzstd is a transitive dependency of libelf, so the -lzstd flag is
strictly necessary only for static builds [1].
Remove ZSTD_LIBS variable, and instead set LIBELF_LIBS depending on
whether the build is static or not. Use $(HOSTPKG_CONFIG) as primary
source of the flags list.
Also add a default value for HOSTPKG_CONFIG in case it's not built via
the toplevel Makefile. Pass it from selftests/bpf too.
[1] https://lore.kernel.org/bpf/4ff82800-2daa-4b9f-95a9-6f512859ee70@linux.dev/
Reported-by: BPF CI Bot (Claude Opus 4.6) <bot+bpf-ci@kernel.org>
Reported-by: Vitaly Chikunov <vt@altlinux.org>
Closes: https://lore.kernel.org/bpf/aaWqMcK-2AQw5dx8@altlinux.org/
Fixes: 4021848a903e ("selftests/bpf: Pass through build flags to bpftool and resolve_btfids")
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Reviewed-by: Paul Chaignon <paul.chaignon@gmail.com>
Link: https://lore.kernel.org/r/20260305014730.3123382-1-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
The check if the initial mapping is sufficient needs to happen much
earlier during bootup. Move this test directly to the start_parisc()
function and use native PDC iodc functions to print the warning, because
panic() and printk() are not functional yet.
This fixes boot when enabling various KALLSYSMS options which need
much more space.
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: <stable@vger.kernel.org> # v6.0+
Pull kvm fixes from Paolo Bonzini:
"Arm:
- Make sure we don't leak any S1POE state from guest to guest when
the feature is supported on the HW, but not enabled on the host
- Propagate the ID registers from the host into non-protected VMs
managed by pKVM, ensuring that the guest sees the intended feature
set
- Drop double kern_hyp_va() from unpin_host_sve_state(), which could
bite us if we were to change kern_hyp_va() to not being idempotent
- Don't leak stage-2 mappings in protected mode
- Correctly align the faulting address when dealing with single page
stage-2 mappings for PAGE_SIZE > 4kB
- Fix detection of virtualisation-capable GICv5 IRS, due to the
maintainer being obviously fat fingered... [his words, not mine]
- Remove duplication of code retrieving the ASID for the purpose of
S1 PT handling
- Fix slightly abusive const-ification in vgic_set_kvm_info()
Generic:
- Remove internal Kconfigs that are now set on all architectures
- Remove per-architecture code to enable KVM_CAP_SYNC_MMU, all
architectures finally enable it in Linux 7.0"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
KVM: always define KVM_CAP_SYNC_MMU
KVM: remove CONFIG_KVM_GENERIC_MMU_NOTIFIER
KVM: arm64: Deduplicate ASID retrieval code
irqchip/gic-v5: Fix inversion of IRS_IDR0.virt flag
KVM: arm64: Revert accidental drop of kvm_uninit_stage2_mmu() for non-NV VMs
KVM: arm64: Fix protected mode handling of pages larger than 4kB
KVM: arm64: vgic: Handle const qualifier from gic_kvm_info allocation type
KVM: arm64: Remove redundant kern_hyp_va() in unpin_host_sve_state()
KVM: arm64: Fix ID register initialization for non-protected pKVM guests
KVM: arm64: Optimise away S1POE handling when not supported by host
KVM: arm64: Hide S1POE from guests when not supported by the host
This leak will cause a hang when tearing down the SCSI host. For example,
iscsid hangs with the following call trace:
[130120.652718] scsi_alloc_sdev: Allocation failure during SCSI scanning, some SCSI devices might not be configured
PID: 2528 TASK: ffff9d0408974e00 CPU: 3 COMMAND: "iscsid"
#0 [ffffb5b9c134b9e0] __schedule at ffffffff860657d4
#1 [ffffb5b9c134ba28] schedule at ffffffff86065c6f
#2 [ffffb5b9c134ba40] schedule_timeout at ffffffff86069fb0
#3 [ffffb5b9c134bab0] __wait_for_common at ffffffff8606674f
#4 [ffffb5b9c134bb10] scsi_remove_host at ffffffff85bfe84b
#5 [ffffb5b9c134bb30] iscsi_sw_tcp_session_destroy at ffffffffc03031c4 [iscsi_tcp]
#6 [ffffb5b9c134bb48] iscsi_if_recv_msg at ffffffffc0292692 [scsi_transport_iscsi]
#7 [ffffb5b9c134bb98] iscsi_if_rx at ffffffffc02929c2 [scsi_transport_iscsi]
#8 [ffffb5b9c134bbf0] netlink_unicast at ffffffff85e551d6
#9 [ffffb5b9c134bc38] netlink_sendmsg at ffffffff85e554ef
Fixes: 8fe4ce5836e9 ("scsi: core: Fix a use-after-free")
Cc: stable@vger.kernel.org
Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://patch.msgid.link/20260223232728.93350-1-junxiao.bi@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Pull tracing fixes from Steven Rostedt:
- Fix possible NULL pointer dereference in trace_data_alloc()
On the trace_data_alloc() error path, it can call trigger_data_free()
with a NULL pointer. This used to be a kfree() but was changed to
trigger_data_free() to clean up any partial initialization. The issue
is that trigger_data_free() does not expect a NULL pointer. Have
trigger_data_free() return safely on NULL pointer.
- Fix multiple events on the command line and bootconfig
If multiple events are enabled on the command line separately and not
grouped, only the last event gets enabled. That is:
trace_event=sched_switch trace_event=sched_waking
will only enable sched_waking whereas:
trace_event=sched_switch,sched_waking
will enable both.
The bootconfig makes it even worse as the second way is the more
common method.
The issue is that a temporary buffer is used to store the events to
enable later in boot. Each time the cmdline callback is called, it
overwrites what was previously there.
Have the callback append the next value (delimited by a comma) if the
temporary buffer already has content.
- Fix command line trace_buffer_size if >= 2G
The logic to allocate the trace buffer uses "int" for the size
parameter in the command line code causing overflow issues if more
that 2G is specified.
* tag 'trace-v7.0-rc2-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: Fix trace_buf_size= cmdline parameter with sizes >= 2G
tracing: Fix enabling multiple events on the kernel command line and bootconfig
tracing: Add NULL pointer check to trigger_data_free()