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Yu Kuai 6636e16e60 block, bfq: release cgroup stats with bfq_group
BFQ cgroup stats contain percpu counters embedded in struct bfq_group,
but the old free path destroys them from bfq_pd_free(), which is tied
to blkg policy-data teardown.

That is not the same lifetime as struct bfq_group. BFQ pins bfq_group
while bfq_queue entities refer to it, so bfq_pd_free() can drop the
policy-data reference while other bfq_group references still exist. The
following blkcg change also defers policy-data release through RCU and
leaves BFQ to run the final bfqg_put() from an RCU callback. For that
conversion, stats teardown must belong to the last bfq_group put, not to
policy-data teardown.

Move stats teardown to bfqg_put() so the embedded counters are destroyed
exactly when the last bfq_group reference is released, before kfree(bfqg).

Without this preparatory change, the RCU-delayed policy-data free
conversion reproduced the following KASAN report:

  BUG: KASAN: slab-use-after-free in percpu_counter_destroy_many+0xf1/0x2e0
  Write of size 8 at addr ffff88811d9409e0 by task test_blkcg/535

  CPU: 0 UID: 0 PID: 535 Comm: test_blkcg Not tainted 7.1.0-rc2-g1e14adca0199 #1 PREEMPT  ea13f83d4b74a12510d20db4a7d9a0fe8275f05c
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-5.fc42 04/01/2014
  Call Trace:
   <TASK>
   dump_stack_lvl+0x54/0x70
   print_address_description+0x77/0x200
   ? percpu_counter_destroy_many+0xf1/0x2e0
   print_report+0x64/0x70
   kasan_report+0x118/0x150
   ? percpu_counter_destroy_many+0xf1/0x2e0
   percpu_counter_destroy_many+0xf1/0x2e0
   __mmdrop+0x1d8/0x350
   finish_task_switch+0x3f5/0x570
   __schedule+0xe8e/0x18a0
   schedule+0xfe/0x1c0
   schedule_timeout+0x7f/0x1d0
   __wait_for_common+0x26c/0x3f0
   wait_for_completion_state+0x21/0x40
   call_usermodehelper_exec+0x271/0x2c0
   __request_module+0x296/0x410
   elv_iosched_store+0x1bc/0x2c0
   queue_attr_store+0x152/0x1c0
   kernfs_fop_write_iter+0x1d7/0x280
   vfs_write+0x580/0x630
   ksys_write+0xec/0x190
   do_syscall_64+0x156/0x490
   entry_SYSCALL_64_after_hwframe+0x77/0x7f

  Allocated by task 535:
   kasan_save_track+0x3e/0x80
   __kasan_kmalloc+0x72/0x90
   bfq_pd_alloc+0x60/0x100 [bfq]
   blkg_create+0x3bb/0xbe0
   blkg_lookup_create+0x3a2/0x460
   blkg_conf_start+0x24a/0x2d0
   bfq_io_set_weight+0x17f/0x430 [bfq]
   cgroup_file_write+0x1c5/0x4b0
   kernfs_fop_write_iter+0x1d7/0x280
   vfs_write+0x580/0x630
   ksys_write+0xec/0x190
   do_syscall_64+0x156/0x490
   entry_SYSCALL_64_after_hwframe+0x77/0x7f

  Freed by task 0:
   kasan_save_track+0x3e/0x80
   kasan_save_free_info+0x46/0x50
   __kasan_slab_free+0x3a/0x60
   kfree+0x14e/0x4f0
   rcu_core+0x6f3/0xcd0
   handle_softirqs+0x1a0/0x550
   __irq_exit_rcu+0x8c/0x150
   irq_exit_rcu+0xe/0x20
   sysvec_apic_timer_interrupt+0x6e/0x80
   asm_sysvec_apic_timer_interrupt+0x1a/0x20

  Last potentially related work creation:
   kasan_save_stack+0x3e/0x60
   kasan_record_aux_stack+0x99/0xb0
   call_rcu+0x55/0x5c0
   blkg_free_workfn+0x130/0x220
   process_scheduled_works+0x655/0xb60
   worker_thread+0x446/0x600
   kthread+0x1f4/0x230
   ret_from_fork+0x259/0x420
   ret_from_fork_asm+0x1a/0x30

Signed-off-by: Yu Kuai <yukuai@fygo.io>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260601061502.899552-1-yukuai@fygo.io
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2026-06-02 07:24:58 -06:00
arch sh fixes for v7.1 2026-05-03 08:58:42 -07:00
block block, bfq: release cgroup stats with bfq_group 2026-06-02 07:24:58 -06:00
certs Clang build fixes for 7.1 2026-04-24 09:29:51 -07:00
crypto This push contains the following changes: 2026-05-02 12:31:43 -07:00
Documentation block: Include bvec.h kernel-doc in the htmldocs 2026-05-29 05:34:25 -06:00
drivers Merge tag 'md-7.2-20260531' of https://git.kernel.org/pub/scm/linux/kernel/git/mdraid/linux into for-7.2/block 2026-06-01 12:52:20 -06:00
fs direct-io: remove IOCB_NOWAIT support 2026-05-26 11:01:55 -06:00
include block: Include bvec.h kernel-doc in the htmldocs 2026-05-29 05:34:25 -06:00
init memblock: updates for 7.0-rc1 2026-04-18 11:29:14 -07:00
io_uring block: Add bvec_folio() 2026-05-29 05:34:24 -06:00
ipc Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
kernel Fix lockup in requeue-PI during signal/timeout wakeups, 2026-05-03 08:17:09 -07:00
lib 20 hotfixes. All are for MM (and for MMish maintainers). 9 are cc:stable 2026-05-01 08:45:23 -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 block: Add bvec_folio() 2026-05-29 05:34:24 -06:00
net net/sched: cls_flower: revert unintended changes 2026-04-30 13:47:01 +02:00
rust rust: block: fix GenDisk cleanup paths 2026-05-31 19:45:06 -06:00
samples soc: drivers for 7.1 2026-04-16 20:34:34 -07:00
scripts First round of Kbuild fixes for 7.1 2026-04-25 17:04:15 -07:00
security selinux: fix avdcache auditing 2026-04-28 18:13:58 -04:00
sound ALSA: hda/tas2781: Fix incorrect bit update for non-book-zero or book 0 pages >1 2026-04-29 07:51:17 +02:00
tools Assorted arm64, ACPI and kselftest fixes for 7.1-rc2: 2026-05-01 16:32:42 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt Arm: 2026-04-17 07:18:03 -07:00
.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 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 kbuild: rust: provide an option to inline C helpers into Rust 2026-03-30 02:03:52 +02:00
.mailmap drm fixes for 7.1-rc2 2026-05-01 16:56:08 -07:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml
COPYING
CREDITS Delete some obsolete networking code 2026-04-24 09:41:58 -07:00
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 Merge tag 'md-7.2-20260531' of https://git.kernel.org/pub/scm/linux/kernel/git/mdraid/linux into for-7.2/block 2026-06-01 12:52:20 -06:00
Makefile Linux 7.1-rc2 2026-05-03 14:21:25 -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