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Chen Cheng 55b77337bd md/raid5: avoid R5_Overlap races while breaking stripe batches
KCSAN report a race in break_stripe_batch_list() vs. raid5_make_request()
on sh->dev[i].flags (plain word write vs. atomic bit op)..

and .. one possible scenario is:

CPU1                            CPU2
break_stripe_batch_list(sh1)
-> handle sh2
-> lock(sh2)
-> sh2->batch_head = NULL
-> unlock(sh2)
-> test_and_clear_bit(R5_Overlap, sh2->dev[i].flags)
-> wake_up_bit(sh2->dev[i].flags)
                                raid5_make_request()
                                -> add_all_stripe_bios(sh2)
                                -> lock(sh2)
                                -> stripe_bio_overlaps(sh2) returns true
				   batch_head is NULL, so new bio overlap
				   exist bio on sh2 -> true
                                -> set_bit(R5_Overlap, sh2->dev[i].flags)
                                -> unlock(sh2)
                                -> wait_on_bit(sh2->dev[i].flags)
-> sh2->dev[i].flags = sh1->dev[i].flags & ~R5_Overlap

No wait_up_bit(), CPU2 could be wait_on_bit() forever...

Fix by :
- Expand the protect zone.
- Use batch_head's device flag's snaphot when no held head_sh->stripe_lock.
- Move sh/head_sh->batch_head = NULL to the end of protected zone , and ,
  any concurrent add_all_stripe_bios() grabs sh->stripe_lock now either:
	- see batch_head != null, and , is rejected by stripe_bio_overlaps()
	  under the lock (no R5_Overlap wait ) , or ,
	- sees batch_head == NULL, only after dev[i].flags has already been
	  set and the prior R5_Overlap waiters worken.

KCSAN report:
================================================
  BUG: KCSAN: data-race in break_stripe_batch_list / raid5_make_request

  write (marked) to 0xffff8e89c8117548 of 8 bytes by task 4042 on cpu 0:
    raid5_make_request+0xea0/0x2930
    md_handle_request+0x4a2/0xa40
    md_submit_bio+0x109/0x1a0
    __submit_bio+0x2ec/0x390
    submit_bio_noacct_nocheck+0x457/0x710
    submit_bio_noacct+0x2a7/0xc20
    submit_bio+0x56/0x250
    blkdev_direct_IO+0x54c/0xda0
    blkdev_write_iter+0x38f/0x570
    aio_write+0x22b/0x490
    io_submit_one+0xa51/0xf70
    __x64_sys_io_submit+0xf7/0x220
    x64_sys_call+0x1907/0x1c60
    do_syscall_64+0x130/0x570
    entry_SYSCALL_64_after_hwframe+0x76/0x7e

  read to 0xffff8e89c8117548 of 8 bytes by task 4010 on cpu 5:
    break_stripe_batch_list+0x249/0x480
    handle_stripe_clean_event+0x720/0x9b0
    handle_stripe+0x32fb/0x4500
    handle_active_stripes.isra.0+0x6e0/0xa50
    raid5d+0x7e0/0xba0
    md_thread+0x15a/0x2d0
    kthread+0x1e3/0x220
    ret_from_fork+0x37a/0x410
    ret_from_fork_asm+0x1a/0x30

  value changed: 0x0000000000000019 -> 0x0000000000000099 --> R5_Overlap

Fixes: fb642b92c2 ("md/raid5: duplicate some more handle_stripe_clean_event code in break_stripe_batch_list")

Signed-off-by: Chen Cheng <chencheng@fnnas.com>
Link: https://patch.msgid.link/20260619041013.1207148-1-chencheng@fnnas.com
Signed-off-by: Yu Kuai <yukuai@fygo.io>
2026-06-23 09:44:11 +08:00
arch CRC updates for 7.2 2026-06-16 09:16:37 +05:30
block block: respect iov_iter::nofault flag in bio_iov_iter_bounce_write() 2026-06-16 14:48:35 -06:00
certs Clang build fixes for 7.1 2026-04-24 09:29:51 -07:00
crypto CRC updates for 7.2 2026-06-16 09:16:37 +05:30
Documentation RTLA patches for v7.2 2026-06-16 17:50:34 +05:30
drivers md/raid5: avoid R5_Overlap races while breaking stripe batches 2026-06-23 09:44:11 +08:00
fs for-7.2/block-20260615 2026-06-16 13:02:47 +05:30
include block: invalidate cached plug timestamp after task switch 2026-06-16 10:07:36 -06:00
init Bootconfig updates for v7.2 2026-06-16 17:29:24 +05:30
io_uring for-7.2/block-20260615 2026-06-16 13:02:47 +05:30
ipc kernel-7.2-rc1.misc 2026-06-15 03:05:50 +05:30
kernel block: invalidate cached plug timestamp after task switch 2026-06-16 10:07:36 -06:00
lib Bootconfig updates for v7.2 2026-06-16 17:29:24 +05:30
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
mm for-7.2/block-20260615 2026-06-16 13:02:47 +05:30
net This update includes the following changes: 2026-06-16 09:01:23 +05:30
rust for-7.2/block-20260615 2026-06-16 13:02:47 +05:30
samples Driver core changes for 7.2-rc1 2026-06-15 12:41:17 +05:30
scripts linux_kselftest-kunit-7.2-rc1 2026-06-16 16:33:57 +05:30
security Kbuild / Kconfig changes for 7.2 2026-06-15 05:01:15 +05:30
sound gpio updates for v7.2-rc1 2026-06-16 07:30:52 +05:30
tools RTLA patches for v7.2 2026-06-16 17:50:34 +05:30
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt vfs-7.2-rc1.misc 2026-06-15 03:59:45 +05:30
.clang-format Devicetree updates for v7.0: 2026-02-11 18:27:08 -08:00
.clippy.toml rust: bump Clippy's MSRV and clean incompatible_msrv allows 2026-04-07 09:51:39 +02:00
.cocciconfig
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add Askar 2026-04-15 02:15:02 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Rust changes for v7.2 2026-06-15 09:25:48 +05:30
.mailmap MAINTAINERS: update Baoquan He's email address 2026-06-03 16:25:50 -07:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml
COPYING
CREDITS fbdev fixes & cleanups for 7.2-rc1: 2026-06-16 08:28:41 +05:30
Kbuild checksyscalls: move instance functionality into generic code 2026-04-05 09:21:32 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS for-7.2/block-20260615 2026-06-16 13:02:47 +05:30
Makefile slab changes for 7.2 2026-06-16 08:44:43 +05:30
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -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