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 btrfs fixes from David Sterba:
"One-liner or short fixes for minor/moderate problems reported recently:
- fixes or level adjustments of error messages
- fix leaked transaction handles after aborted transactions, when
using the remap tree feature
- fix a few leaked chunk maps after errors
- fix leaked page array in io_uring encoded read if an error occurs
and the 'finished' is not called
- fix double release of reserved extents when doing a range COW
- don't commit super block when the filesystem is in shutdown state
- fix squota accounting condition when checking members vs parent
usage
- other error handling fixes"
* tag 'for-7.0-rc2-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux:
btrfs: check block group lookup in remove_range_from_remap_tree()
btrfs: fix transaction handle leaks in btrfs_last_identity_remap_gone()
btrfs: fix chunk map leak in btrfs_map_block() after btrfs_translate_remap()
btrfs: fix chunk map leak in btrfs_map_block() after btrfs_chunk_map_num_copies()
btrfs: fix compat mask in error messages in btrfs_check_features()
btrfs: print correct subvol num if active swapfile prevents deletion
btrfs: fix warning in scrub_verify_one_metadata()
btrfs: fix objectid value in error message in check_extent_data_ref()
btrfs: fix incorrect key offset in error message in check_dev_extent_item()
btrfs: fix error message order of parameters in btrfs_delete_delayed_dir_index()
btrfs: don't commit the super block when unmounting a shutdown filesystem
btrfs: free pages on error in btrfs_uring_read_extent()
btrfs: fix referenced/exclusive check in squota_check_parent_usage()
btrfs: remove pointless WARN_ON() in cache_save_setup()
btrfs: convert log messages to error level in btrfs_replay_log()
btrfs: remove btrfs_handle_fs_error() after failure to recover log trees
btrfs: remove redundant warning message in btrfs_check_uuid_tree()
btrfs: change warning messages to error level in open_ctree()
btrfs: fix a double release on reserved extents in cow_one_range()
btrfs: handle discard errors in in btrfs_finish_extent_commit()
If a 'const struct foo __user *ptr' is used for the address passed to
scoped_user_read_access() then you get a warning/error
uaccess.h:691:1: error: initialization discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
for the
void __user *_tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl)
assignment.
Fix by using 'auto' for both _tmpptr and the redeclaration of uptr.
Replace the CLASS() with explicit __cleanup() functions on uptr.
Fixes: e497310b4ffb ("uaccess: Provide scoped user access regions")
Signed-off-by: David Laight <david.laight.linux@gmail.com>
Reviewed-and-tested-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add a check in remove_range_from_remap_tree() after we call
btrfs_lookup_block_group(), to check if it is NULL. This shouldn't
happen, but if it does we at least get an error rather than a segfault.
Reported-by: Chris Mason <clm@fb.com>
Link: https://lore.kernel.org/linux-btrfs/20260125125129.2245240-1-clm@meta.com/
Fixes: 979e1dc3d69e ("btrfs: handle deletions from remapped block group")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Mark Harmstone <mark@harmstone.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Pull nfsd fixes from Chuck Lever:
- Restore previous nfsd thread count reporting behavior
- Fix credential reference leaks in the NFSD netlink admin protocol
* tag 'nfsd-7.0-1' of git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux:
nfsd: report the requested maximum number of threads instead of number running
nfsd: Fix cred ref leak in nfsd_nl_listener_set_doit().
nfsd: Fix cred ref leak in nfsd_nl_threads_set_doit().
btrfs_abort_transaction(), unlike btrfs_commit_transaction(), doesn't
also free the transaction handle. Fix the instances in
btrfs_last_identity_remap_gone() where we're also leaking the
transaction on abort.
Reported-by: Chris Mason <clm@fb.com>
Link: https://lore.kernel.org/linux-btrfs/20260125125129.2245240-1-clm@meta.com/
Fixes: 979e1dc3d69e ("btrfs: handle deletions from remapped block group")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Mark Harmstone <mark@harmstone.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
The current netlink and /proc interfaces deviate from their traditional
values when dynamic threading is enabled, and there is currently no way
to know what the current setting is. This patch brings the reporting
back in line with traditional behavior.
Make these interfaces report the requested maximum number of threads
instead of the number currently running. Also, update documentation and
comments to reflect that this value represents a maximum and not the
number currently running.
Fixes: d8316b837c2c ("nfsd: add controls to set the minimum number of threads per pool")
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
If the call to btrfs_translate_remap() in btrfs_map_block() returns an
error code, we were leaking the chunk map. Fix it by jumping to out
rather than returning directly.
Reported-by: Chris Mason <clm@fb.com>
Link: https://lore.kernel.org/linux-btrfs/20260125125830.2352988-1-clm@meta.com/
Fixes: 18ba64992871 ("btrfs: redirect I/O for remapped block groups")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Mark Harmstone <mark@harmstone.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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
nfsd_nl_listener_set_doit() uses get_current_cred() without
put_cred().
As we can see from other callers, svc_xprt_create_from_sa()
does not require the extra refcount.
nfsd_nl_listener_set_doit() is always in the process context,
sendmsg(), and current->cred does not go away.
Let's use current_cred() in nfsd_nl_listener_set_doit().
Fixes: 16a471177496 ("NFSD: add listener-{set,get} netlink command")
Cc: stable@vger.kernel.org
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Fix a chunk map leak in btrfs_map_block(): if we return early with -EINVAL,
we're not freeing the chunk map that we've just looked up.
Fixes: 0ae653fbec2b ("btrfs: reduce chunk_map lookups in btrfs_map_block()")
CC: stable@vger.kernel.org # 6.12+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Mark Harmstone <mark@harmstone.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Pull debugobjects fix from Thomas Gleixner:
"A single fix for debugobjects.
The deferred page initialization prevents debug objects from
allocating slab pages until the initialization is complete. That
causes depletion of the pool and disabling of debugobjects.
The reason is that debugobjects uses __GFP_HIGH for allocations as it
might be invoked from arbitrary contexts. When PREEMPT_COUNT is
disabled there is no way to know whether the context is safe to set
__GFP_KSWAPD_RECLAIM.
This worked until v6.18. Since then allocations w/o a reclaim flag
cause new_slab() to end up in alloc_frozen_pages_nolock_noprof(),
which returns early when deferred page initialization has not yet
completed.
Work around that when PREEMPT_COUNT is enabled as the preempt counter
allows debugobjects to add __GFP_KSWAPD_RECLAIM to the GFP flags when
the context is preemtible. When PREEMPT_COUNT is disabled the context
is unknown and the reclaim bit can't be set because the caller might
hold locks which might deadlock in the allocator.
That makes debugobjects depend on PREEMPT_COUNT ||
!DEFERRED_STRUCT_PAGE_INIT, which limits the coverage slightly, but
keeps it functional for most cases"
* tag 'core-debugobjects-2026-03-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
debugobject: Make it work with deferred page initialization - again
KVM/arm64 fixes for 7.0, take #1
- 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...
- Remove duplication of code retrieving the ASID for the purpose of
S1 PT handling
- Fix slightly abusive const-ification in vgic_set_kvm_info()
syzbot reported memory leak of struct cred. [0]
nfsd_nl_threads_set_doit() passes get_current_cred() to
nfsd_svc(), but put_cred() is not called after that.
The cred is finally passed down to _svc_xprt_create(),
which calls get_cred() with the cred for struct svc_xprt.
The ownership of the refcount by get_current_cred() is not
transferred to anywhere and is just leaked.
nfsd_svc() is also called from write_threads(), but it does
not bump file->f_cred there.
nfsd_nl_threads_set_doit() is called from sendmsg() and
current->cred does not go away.
Let's use current_cred() in nfsd_nl_threads_set_doit().
[0]:
BUG: memory leak
unreferenced object 0xffff888108b89480 (size 184):
comm "syz-executor", pid 5994, jiffies 4294943386
hex dump (first 32 bytes):
01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace (crc 369454a7):
kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
slab_post_alloc_hook mm/slub.c:4958 [inline]
slab_alloc_node mm/slub.c:5263 [inline]
kmem_cache_alloc_noprof+0x412/0x580 mm/slub.c:5270
prepare_creds+0x22/0x600 kernel/cred.c:185
copy_creds+0x44/0x290 kernel/cred.c:286
copy_process+0x7a7/0x2870 kernel/fork.c:2086
kernel_clone+0xac/0x6e0 kernel/fork.c:2651
__do_sys_clone+0x7f/0xb0 kernel/fork.c:2792
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Fixes: 924f4fb003ba ("NFSD: convert write_threads to netlink command")
Cc: stable@vger.kernel.org
Reported-by: syzbot+dd3b43aa0204089217ee@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/69744674.a00a0220.33ccc7.0000.GAE@google.com/
Tested-by: syzbot+dd3b43aa0204089217ee@syzkaller.appspotmail.com
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Commit d7f67ac9a928 ("btrfs: relax block-group-tree feature dependency
checks") introduced a regression when it comes to handling unsupported
incompat or compat_ro flags. Beforehand we only printed the flags that
we didn't recognize, afterwards we printed them all, which is less
useful. Fix the error handling so it behaves like it used to.
Fixes: d7f67ac9a928 ("btrfs: relax block-group-tree feature dependency checks")
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Mark Harmstone <mark@harmstone.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Pull x86 fixes from Ingo Molnar:
- Fix speculative safety in fred_extint()
- Fix __WARN_printf() trap in early_fixup_exception()
- Fix clang-build boot bug for unusual alignments, triggered by
CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B=y
- Replace the final few __ASSEMBLY__ stragglers that snuck in lately
into non-UAPI x86 headers and use __ASSEMBLER__ consistently (again)
* tag 'x86-urgent-2026-03-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/headers: Replace __ASSEMBLY__ stragglers with __ASSEMBLER__
x86/cfi: Fix CFI rewrite for odd alignments
x86/bug: Handle __WARN_printf() trap in early_fixup_exception()
x86/fred: Correct speculative safety in fred_extint()