Dmitry Antipov 82ea9d4fc0 ocfs2: always run deallocs on copy-on-write completion
Local fuzzing of 6.12.94 has found the following memory leak
caused by doing 'copy_file_range()' within the same filesystem:

unreferenced object 0xffff88812192c980 (size 32):
  comm "syz.0.49", pid 12095, jiffies 4294964143
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00  ................
    c0 c5 92 21 81 88 ff ff 00 02 00 00 00 06 00 00  ...!............
  backtrace (crc 7068d63f):
    kmemleak_alloc_recursive include/linux/kmemleak.h:42 [inline]
    slab_post_alloc_hook mm/slub.c:4152 [inline]
    slab_alloc_node mm/slub.c:4197 [inline]
    __kmalloc_cache_noprof+0x168/0x2c0 mm/slub.c:4358
    kmalloc_noprof include/linux/slab.h:878 [inline]
    ocfs2_find_per_slot_free_list fs/ocfs2/alloc.c:6618 [inline]
    ocfs2_cache_block_dealloc+0x155/0x4b0 fs/ocfs2/alloc.c:6786
    ocfs2_cache_extent_block_free fs/ocfs2/alloc.c:6819 [inline]
    ocfs2_unlink_path+0x286/0x450 fs/ocfs2/alloc.c:2613
    ocfs2_rotate_subtree_left fs/ocfs2/alloc.c:2779 [inline]
    __ocfs2_rotate_tree_left+0x1f6f/0x2da0 fs/ocfs2/alloc.c:2985
    ocfs2_rotate_tree_left+0x283/0xe00 fs/ocfs2/alloc.c:3237
    ocfs2_try_to_merge_extent+0xf56/0x1a20 fs/ocfs2/alloc.c:3825
    ocfs2_split_extent+0x15f4/0x2940 fs/ocfs2/alloc.c:5138
    ocfs2_clear_ext_refcount+0x2f6/0x550 fs/ocfs2/refcounttree.c:3098
    ocfs2_replace_clusters fs/ocfs2/refcounttree.c:3131 [inline]
    ocfs2_make_clusters_writable fs/ocfs2/refcounttree.c:3255 [inline]
    ocfs2_replace_cow+0x991/0x1660 fs/ocfs2/refcounttree.c:3349
    ocfs2_refcount_cow_hunk fs/ocfs2/refcounttree.c:3427 [inline]
    ocfs2_refcount_cow+0x5e1/0x9f0 fs/ocfs2/refcounttree.c:3470
    ocfs2_prepare_inode_for_write fs/ocfs2/file.c:2340 [inline]
    ocfs2_file_write_iter+0xbda/0x1880 fs/ocfs2/file.c:2451
    iter_file_splice_write+0x890/0xf60 fs/splice.c:743
    do_splice_from fs/splice.c:944 [inline]
    direct_splice_actor+0x232/0x480 fs/splice.c:1167
    splice_direct_to_actor+0x4b4/0xb60 fs/splice.c:1111
    do_splice_direct_actor fs/splice.c:1210 [inline]
    do_splice_direct+0x10f/0x1c0 fs/splice.c:1236
    do_sendfile+0x430/0xbf0 fs/read_write.c:1388

unreferenced object 0xffff88812192c5c0 (size 32):
  comm "syz.0.49", pid 12095, jiffies 4294964143
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    29 70 00 00 00 00 00 00 19 00 00 00 00 00 00 00  )p..............
  backtrace (crc afec850f):
    kmemleak_alloc_recursive include/linux/kmemleak.h:42 [inline]
    slab_post_alloc_hook mm/slub.c:4152 [inline]
    slab_alloc_node mm/slub.c:4197 [inline]
    __kmalloc_cache_noprof+0x168/0x2c0 mm/slub.c:4358
    kmalloc_noprof include/linux/slab.h:878 [inline]
    kzalloc_noprof include/linux/slab.h:1014 [inline]
    ocfs2_cache_block_dealloc+0x25c/0x4b0 fs/ocfs2/alloc.c:6793
    ocfs2_cache_extent_block_free fs/ocfs2/alloc.c:6819 [inline]
    ocfs2_unlink_path+0x286/0x450 fs/ocfs2/alloc.c:2613
    ocfs2_rotate_subtree_left fs/ocfs2/alloc.c:2779 [inline]
    __ocfs2_rotate_tree_left+0x1f6f/0x2da0 fs/ocfs2/alloc.c:2985
    ocfs2_rotate_tree_left+0x283/0xe00 fs/ocfs2/alloc.c:3237
    ocfs2_try_to_merge_extent+0xf56/0x1a20 fs/ocfs2/alloc.c:3825
    ocfs2_split_extent+0x15f4/0x2940 fs/ocfs2/alloc.c:5138
    ocfs2_clear_ext_refcount+0x2f6/0x550 fs/ocfs2/refcounttree.c:3098
    ocfs2_replace_clusters fs/ocfs2/refcounttree.c:3131 [inline]
    ocfs2_make_clusters_writable fs/ocfs2/refcounttree.c:3255 [inline]
    ocfs2_replace_cow+0x991/0x1660 fs/ocfs2/refcounttree.c:3349
    ocfs2_refcount_cow_hunk fs/ocfs2/refcounttree.c:3427 [inline]
    ocfs2_refcount_cow+0x5e1/0x9f0 fs/ocfs2/refcounttree.c:3470
    ocfs2_prepare_inode_for_write fs/ocfs2/file.c:2340 [inline]
    ocfs2_file_write_iter+0xbda/0x1880 fs/ocfs2/file.c:2451
    iter_file_splice_write+0x890/0xf60 fs/splice.c:743
    do_splice_from fs/splice.c:944 [inline]
    direct_splice_actor+0x232/0x480 fs/splice.c:1167
    splice_direct_to_actor+0x4b4/0xb60 fs/splice.c:1111
    do_splice_direct_actor fs/splice.c:1210 [inline]
    do_splice_direct+0x10f/0x1c0 fs/splice.c:1236
    do_sendfile+0x430/0xbf0 fs/read_write.c:1388

This happens when 'ocfs2_cache_block_dealloc()' called from
'ocfs2_cache_extent_block_free()' uses the suballocator to
schedule extent removal, so 'ocfs2_run_deallocs()' should
be run unconditionally to complete the removal with
'ocfs2_free_cached_blocks()'. An extra semi-automated static
analysis [1] suspects that the same scenario looks possible in
'ocfs2_attach_refcount_tree()' and 'ocfs2_reflink_remap_blocks()'
as well, but, since 'ocfs2_run_deallocs()' is a safe no-op for
an empty dealloc context, 'ocfs2_create_reflink_node()' and
'ocfs2_reflink_xattrs()' may be adjusted in the same way too,
thus keeping the code pattern consistent.

Link: https://lore.kernel.org/20260721102840.387663-1-dmantipov@yandex.ru
Link: https://lore.kernel.org/ocfs2-devel/f1d7e266-4b44-41b9-98c0-5b3868a8d9c3@yandex.ru [1]
Fixes: 6f70fa5199 ("ocfs2: Add CoW support.")
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Suggested-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2026-08-05 11:20:11 -07:00
2026-08-03 21:10:16 -07:00
2026-01-26 19:07:09 -08:00
2022-09-28 09:02:20 +02:00
2026-07-14 16:34:04 +02:00
2025-02-19 14:53:27 -07:00
2026-07-26 14:45:48 -07:00

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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