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Qu Wenruo 690c2accac btrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock
[FALSE ALERTS]
There is a bug report that the warning inside
invalidate_and_check_btree_folios() got triggered during btrfs/298:

 BTRFS info (device sdd): first mount of filesystem f9bf732a-a19b-44b9-99a7-614ddff168e2
 BTRFS info (device sdd): using crc32c checksum algorithm
 BTRFS error (device sdd): failed to find fsid cb2fdb42-b638-4f2f-badd-4127467ba674 when attempting to open seed devices
 BTRFS error (device sdd): failed to read chunk tree: -2
 ------------[ cut here ]------------
 WARNING: disk-io.c:3342 at invalidate_and_check_btree_folios+0x260/0x3c0 [btrfs], CPU#4: mount/125993
 CPU: 4 UID: 0 PID: 125993 Comm: mount Tainted: G        W  OE       7.1.0-rc7-custom+ #1 PREEMPT(full)
 Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20250812-19.fc42 08/12/2025
 Call trace:
  invalidate_and_check_btree_folios+0x260/0x3c0 [btrfs] (P)
  open_ctree+0x1f50/0x23b0 [btrfs]
  btrfs_get_tree+0x89c/0xc48 [btrfs]
  vfs_get_tree+0x30/0x110
  vfs_cmd_create+0x58/0xe8
  __arm64_sys_fsconfig+0x39c/0x518
  invoke_syscall.constprop.0+0x48/0x120
  el0_svc_common.constprop.0+0x40/0xe8
  do_el0_svc+0x24/0x38
  el0_svc+0x50/0x310
  el0t_64_sync_handler+0xa0/0xe8
  el0t_64_sync+0x198/0x1a0
 ---[ end trace 0000000000000000 ]---
 BTRFS warning (device sdd): unable to release extent buffer 365985792 owner 3 gen 17 refs 3 flags 0x5

[CAUSE]
In that invalidate_and_check_btree_folios() we wait for the eb to finish
its read, then check if it's only held by us and the btree inode.

If not, then do a warning as it may be still held, and could cause
problems.

But there is a small window where the check can lead to false alerts:

    Thread A (Read endio)         |        Thread B (Unmount)
----------------------------------+-------------------------------------
 end_bbio_meta_read()             |
 | The eb has one extra ref held  |
 | by the reader, and has         |
 | EXTENT_BUFFER_READING flag set | invalidate_and_check_btree_folios()
 |                                | |
 |- clear_extent_buffer_reading() | |
 |                                | |- wait_on_bit_io();
 |                                | |  The EXTENT_BUFFER_READING flag is
 |                                | |  cleared
 |                                | |- if (refcount_read(eb->refs) > 2)
 |                                |    The eb is held by the read, us
 |                                |    and btree inode, thus it
 |                                |    will trigger the warning
 |- free_extent_buffer()          |

[FIX]
Introduce a helper, free_extent_buffer_clear_reading().

If the new parameter, @clear_reading, is set, we will hold the spinlock
at the beginning of free_extent_buffer_clear_reading() to make sure the
EXTENT_BUFFER_READING flag is cleared inside the same critical section
of decreasing refs.

Now free_extent_buffer() will just call
free_extent_buffer_clear_reading() with @clear_reading set to false, so
no behavior change.

But for end_bbio_meta_read(), it will not clear_extent_buffer_reading()
directly, but pass @clear_reading as true.

Then inside invalidate_and_check_btree_folios(), hold the refs_lock
before reading refs.
So that we eliminate the race window completely.

Reported-by: Su Yue <glass.su@suse.com>
Link: https://lore.kernel.org/linux-btrfs/DC0C775E-13B3-47D9-9AB2-895BB11C029D@suse.com/
Fixes: 83f7e52b7e ("btrfs: warn about extent buffer that can not be released")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
History 2026-08-07 19:17:17 +02:00
arch s390: 2026-08-07 07:41:40 -07:00
block block: stop the timeout timer when releasing a never added disk 2026-07-29 05:23:20 -06:00
certs treewide: fix indentation and whitespace in Kconfig files 2026-05-28 21:24:42 -07:00
crypto crypto: aes - Fix conditions for selecting MAC dependencies 2026-07-09 11:06:22 -04:00
Documentation Including fixes from netfilter. 2026-08-06 11:39:20 -07:00
drivers s390: 2026-08-07 07:41:40 -07:00
fs btrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock 2026-08-07 19:17:17 +02:00
include Thermal control fixes for 7.2-rc7 2026-08-07 06:48:51 -07:00
init rust: allow suspicious_runtime_symbol_definitions lint for Rust >= 1.98 2026-06-29 13:02:15 +02:00
io_uring io_uring: preserve task restrictions across exec 2026-07-30 14:40:22 -06:00
ipc kernel-7.2-rc1.misc 2026-06-15 03:05:50 +05:30
kernel BPF fixes: 2026-08-07 08:08:57 -07:00
lib hardening fixes for v7.2-rc6 2026-07-28 13:36:01 -07:00
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 17 hotfixes. 15 are cc:stable. 16 are for MM. 2026-08-06 20:29:38 -07:00
net BPF fixes: 2026-08-07 08:08:57 -07:00
rust rust: time: fix as_micros_ceil() to round correctly for negative Delta 2026-07-18 19:07:35 +02:00
samples samples/damon/mtier: error out for zero quota goal target values 2026-08-04 20:02:02 -07:00
scripts kbuild: rpm-pkg: Preserve BTF sections in kernel modules during debuginfo stripping 2026-07-29 16:21:42 -07:00
security selinux/stable-7.2 PR 20260805 2026-08-05 13:40:11 -07:00
sound ALSA: usb-audio: Fix sticky mixer regressions on M-Audio Fast Track Ultra 2026-08-07 10:35:31 +02:00
tools BPF fixes: 2026-08-07 08:08:57 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt KVM/arm64 fixes for 7.2, take #2 2026-07-15 12:13:30 +02:00
.clang-format clang-format: fix formatting of guard() and scoped_guard() statements 2026-05-28 21:24:41 -07:00
.clippy.toml rust: bump Clippy's MSRV and clean incompatible_msrv allows 2026-04-07 09:51:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add myself 2026-04-02 16:48:25 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore SPDX patches for 7.2-rc1 2026-06-22 12:06:22 -07:00
.mailmap 17 hotfixes. 15 are cc:stable. 16 are for MM. 2026-08-06 20:29:38 -07:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS CREDITS: Add Wolfram Sang 2026-07-14 16:34:04 +02:00
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 sound fixes for 7.2-rc7 2026-08-07 06:36:11 -07:00
Makefile Linux 7.2-rc6 2026-08-02 16:24:24 -07:00
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